feat(files): preview attachments via short-lived signed URLs

Downloads require an Authorization header, which <iframe>/<img> cannot
send. The previous blob: workaround broke under download managers (IDM
hooks blob URLs, fails to resolve them, and leaves a 0-byte file) and in
Chrome's mobile emulation, which has no inline PDF plugin.

Backend:
- preview_token.py: HMAC-signed token bound to one (quote, kind, file)
  with a 5-minute TTL, keyed off an existing secret
- GET /quotes/{id}/preview-url/{kind}/{attachment} mints the URL
- the two file GET routes accept a Bearer session OR the signed ?t= token
  (they leave the global auth dep, so the other six file routes now carry
  it explicitly — nothing is open by omission)

Frontend:
- api.files.previewUrl() replaces the blob helper
- shared FilePreviewModal + useFilePreview; FileList and the dashboard
  quote card both use it
- PDFs render with the browser's native viewer on desktop and pdf.js on
  canvas where no inline viewer exists (mobile); pdf.js is fed the bytes
  in memory so no PDF URL is exposed for a download manager to intercept
- removed the per-attachment download buttons on the dashboard card and
  the modal header

Ops:
- nginx: explicit MIME types (.mjs as text/javascript) — a module worker
  served as octet-stream is refused and crashed the page
- frontend service bypasses the nginx entrypoint, whose apk manifest call
  hangs when the package mirror is unreachable (502s)

backend/app/routers/files.py

@@ -17,14 +17,15 @@ import os
 import uuid
 from urllib.parse import quote
 
-from fastapi import APIRouter, Depends, File, Response, UploadFile
+from fastapi import APIRouter, Depends, File, Request, Response, UploadFile
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from app.auth import require_role
+from app.auth import UserContext, get_current_user, get_optional_user, require_role
 from app.db.engine import get_db
 from app.models.procurement import Quote
 from app.services import file_service
-from app.utils.errors import NotFoundError, ValidationError
+from app.utils.errors import NotFoundError, UnauthorizedError, ValidationError
+from app.utils.preview_token import make_preview_token, verify_preview_token
 
 router = APIRouter(prefix="/quotes", tags=["files"])
 
@@ -41,13 +42,17 @@ ALLOWED_EXTENSIONS = {".png", ".jpg", ".jpeg", ".webp", ".gif", ".pdf"}
 MAX_FILE_SIZE_BYTES = 5 * 1024 * 1024
 
 
-def _content_disposition(file_name: str) -> str:
+def _content_disposition(file_name: str, inline: bool = False) -> str:
     """Header-safe Content-Disposition for non-ASCII (e.g. Persian) filenames.
 
     HTTP headers are encoded as latin-1, so a Persian name raises
     UnicodeEncodeError and kills the response. Per RFC 6266 / RFC 5987 the
     UTF-8 name goes percent-encoded in ``filename*``, with an ASCII fallback
     in ``filename`` for old clients.
+
+    ``inline=True`` makes the browser render the file (PDF in a viewer,
+    image in the tab) instead of downloading it — required by the preview
+    modal, whose <iframe> would otherwise trigger a download.
     """
     raw = file_name.encode("ascii", "ignore").decode("ascii")
     # keep the fallback header-safe: no quotes, no control characters
@@ -56,9 +61,37 @@ def _content_disposition(file_name: str) -> str:
     stem = fallback[: -len(ext)].strip() if ext and fallback.lower().endswith(ext.lower()) else fallback
     if not stem or not any(ch.isalnum() for ch in stem):
         # nothing meaningful survived ASCII-folding (e.g. a pure-Persian
-        # name): use a generic attachment name that keeps the extension
-        fallback = f"attachment{ext}" if ext else "attachment"
-    return f"attachment; filename=\"{fallback}\"; filename*=UTF-8''{quote(file_name)}"
+        # name): use a generic name that keeps the extension
+        fallback = f"{'preview' if inline else 'attachment'}{ext}" if ext else (
+            "preview" if inline else "attachment"
+        )
+    kind = "inline" if inline else "attachment"
+    return f"{kind}; filename=\"{fallback}\"; filename*=UTF-8''{quote(file_name)}"
+
+
+async def _require_file_access(
+    request: Request,
+    token: str | None,
+    quote_id: uuid.UUID,
+    kind: str,
+    attachment_id: uuid.UUID,
+    db: AsyncSession,
+) -> None:
+    """Authorise a file read by session header OR a signed ``?t=`` token.
+
+    These two GET routes sit outside the global Bearer dependency because a
+    browser cannot attach an Authorization header to <iframe>/<img> loads.
+    A caller is accepted when it presents either a valid Casdoor session
+    (resolved by get_optional_user) or a signed token scoped to exactly
+    this file, which expires within minutes.
+    """
+    if request is not None and request.headers.get("authorization"):
+        user = await get_optional_user(request, db)
+        if user is not None and user.role is not None:
+            return
+    if token and verify_preview_token(token, quote_id, kind, attachment_id):
+        return
+    raise UnauthorizedError("دسترسی به این فایل مجاز نیست — ابتدا وارد شوید")
 
 
 async def _quote_or_404(db: AsyncSession, quote_id: uuid.UUID) -> Quote:
@@ -92,7 +125,7 @@ async def _attachment_or_404(
 # Invoice — قابل بارگذاری در هر وضعیتی (از صفحه‌ی ویرایش)
 # ---------------------------------------------------------------------------
 
-@router.post("/{quote_id}/invoice", status_code=201)
+@router.post("/{quote_id}/invoice", status_code=201, dependencies=[Depends(get_current_user)])
 async def upload_invoice(quote_id: uuid.UUID, file: UploadFile = File(...), db: AsyncSession = Depends(get_db)):
     await _quote_or_404(db, quote_id)
     mime = _validate_upload(file)
@@ -103,29 +136,67 @@ async def upload_invoice(quote_id: uuid.UUID, file: UploadFile = File(...), db:
     return {"data": stored.to_dict()}
 
 
-@router.get("/{quote_id}/invoice")
+@router.get("/{quote_id}/invoice", dependencies=[Depends(get_current_user)])
 async def list_invoices(quote_id: uuid.UUID, db: AsyncSession = Depends(get_db)):
     await _quote_or_404(db, quote_id)
     attachments = await file_service.list_for(db, quote_id, "invoice")
     return {"data": [a.to_dict() for a in attachments]}
 
 
+# ---------------------------------------------------------------------------
+# Preview URL — a real, short-lived URL the browser can load in an
+# <iframe>/<img> (which cannot send an Authorization header). Using a real
+# URL instead of a blob: avoids download managers that hijack blob URLs and
+# leave 0-byte files behind.
+# ---------------------------------------------------------------------------
+@router.get("/{quote_id}/preview-url/{kind}/{attachment_id}")
+async def preview_url(
+    quote_id: uuid.UUID,
+    kind: str,
+    attachment_id: uuid.UUID,
+    db: AsyncSession = Depends(get_db),
+    _ctx: UserContext = Depends(get_current_user),
+):
+    if kind not in ("invoice", "proforma"):
+        raise ValidationError("نوع پیوست نامعتبر است", field="kind")
+    await _quote_or_404(db, quote_id)
+    await _attachment_or_404(db, quote_id, attachment_id, kind)
+    token = make_preview_token(quote_id, kind, attachment_id)
+    # مسیر نسبی برگردانده می‌شود؛ فرانت با BASE_URL خودش کاملش می‌کند
+    return {
+        "data": {
+            "url": f"/quotes/{quote_id}/{kind}/{attachment_id}?disposition=inline&t={token}",
+            "token": token,
+        }
+    }
+
+
 @router.get("/{quote_id}/invoice/{attachment_id}")
-async def download_invoice(quote_id: uuid.UUID, attachment_id: uuid.UUID, db: AsyncSession = Depends(get_db)):
+async def download_invoice(
+    quote_id: uuid.UUID,
+    attachment_id: uuid.UUID,
+    disposition: str = "attachment",
+    t: str | None = None,
+    request: Request = None,
+    db: AsyncSession = Depends(get_db),
+):
     await _quote_or_404(db, quote_id)
     attachment = await _attachment_or_404(db, quote_id, attachment_id, "invoice")
+    await _require_file_access(request, t, quote_id, "invoice", attachment_id, db)
     content = await file_service.read_bytes(attachment)
     return Response(
         content=content,
         media_type=attachment.mime_type,
         headers={
-            "Content-Disposition": _content_disposition(attachment.file_name),
+            "Content-Disposition": _content_disposition(
+                attachment.file_name, inline=disposition == "inline"
+            ),
             "X-File-Id": str(attachment.id),
         },
     )
 
 
-@router.delete("/{quote_id}/invoice/{attachment_id}", dependencies=[Depends(_attachment_deleter)])
+@router.delete("/{quote_id}/invoice/{attachment_id}", dependencies=[Depends(_attachment_deleter), Depends(get_current_user)])
 async def delete_invoice(quote_id: uuid.UUID, attachment_id: uuid.UUID, db: AsyncSession = Depends(get_db)):
     await _quote_or_404(db, quote_id)
     attachment = await _attachment_or_404(db, quote_id, attachment_id, "invoice")
@@ -137,7 +208,7 @@ async def delete_invoice(quote_id: uuid.UUID, attachment_id: uuid.UUID, db: Asyn
 # Proforma — no status restriction
 # ---------------------------------------------------------------------------
 
-@router.post("/{quote_id}/proforma", status_code=201)
+@router.post("/{quote_id}/proforma", status_code=201, dependencies=[Depends(get_current_user)])
 async def upload_proforma(quote_id: uuid.UUID, file: UploadFile = File(...), db: AsyncSession = Depends(get_db)):
     await _quote_or_404(db, quote_id)
     mime = _validate_upload(file)
@@ -148,7 +219,7 @@ async def upload_proforma(quote_id: uuid.UUID, file: UploadFile = File(...), db:
     return {"data": stored.to_dict()}
 
 
-@router.get("/{quote_id}/proforma")
+@router.get("/{quote_id}/proforma", dependencies=[Depends(get_current_user)])
 async def list_proformas(quote_id: uuid.UUID, db: AsyncSession = Depends(get_db)):
     await _quote_or_404(db, quote_id)
     attachments = await file_service.list_for(db, quote_id, "proforma")
@@ -156,21 +227,31 @@ async def list_proformas(quote_id: uuid.UUID, db: AsyncSession = Depends(get_db)
 
 
 @router.get("/{quote_id}/proforma/{attachment_id}")
-async def download_proforma(quote_id: uuid.UUID, attachment_id: uuid.UUID, db: AsyncSession = Depends(get_db)):
+async def download_proforma(
+    quote_id: uuid.UUID,
+    attachment_id: uuid.UUID,
+    disposition: str = "attachment",
+    t: str | None = None,
+    request: Request = None,
+    db: AsyncSession = Depends(get_db),
+):
     await _quote_or_404(db, quote_id)
     attachment = await _attachment_or_404(db, quote_id, attachment_id, "proforma")
+    await _require_file_access(request, t, quote_id, "proforma", attachment_id, db)
     content = await file_service.read_bytes(attachment)
     return Response(
         content=content,
         media_type=attachment.mime_type,
         headers={
-            "Content-Disposition": _content_disposition(attachment.file_name),
+            "Content-Disposition": _content_disposition(
+                attachment.file_name, inline=disposition == "inline"
+            ),
             "X-File-Id": str(attachment.id),
         },
     )
 
 
-@router.delete("/{quote_id}/proforma/{attachment_id}", dependencies=[Depends(_attachment_deleter)])
+@router.delete("/{quote_id}/proforma/{attachment_id}", dependencies=[Depends(_attachment_deleter), Depends(get_current_user)])
 async def delete_proforma(quote_id: uuid.UUID, attachment_id: uuid.UUID, db: AsyncSession = Depends(get_db)):
     await _quote_or_404(db, quote_id)
     attachment = await _attachment_or_404(db, quote_id, attachment_id, "proforma")