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)

frontend/src/pages/Dashboard/QuoteDetail.tsx

@@ -13,6 +13,7 @@ import { fmtDate, fmtDateTime, fmtNum } from "../../lib/formatters";
 import { groupCommas } from "../../lib/numutil";
 import { FlowDiagram, type FlowRefs } from "./FlowDiagram";
 import { itemProjects } from "../../lib/quoteUtils";
+import { FilePreviewModal, useFilePreview } from "../../components/FilePreviewModal";
 
 export interface QuoteDetailProps {
   store: Store;
@@ -25,6 +26,15 @@ export function QuoteDetail({ store, q }: QuoteDetailProps) {
   const [flowRefs] = useState<FlowRefs>(() => ({ items: new Map(), termsheets: new Map() }));
   const [bump, setBump] = useState(0);
 
+  // پیش‌نمایش پیوست‌ها: کلیک روی نام فایل، فایل را نشان می‌دهد (نه دانلود).
+  // بایت‌ها با توکن گرفته می‌شوند چون <img>/<iframe> نمی‌توانند هدر بفرستند.
+  // کلید با پیشوند نوع پیوست ساخته می‌شود تا نوعش گم نشود.
+  const preview = useFilePreview((key, name) => {
+    const [kind, id] = key.split(":") as ["invoice" | "proforma", string];
+    void name;
+    return api.files.previewUrl(q.id, kind, id);
+  });
+
   useEffect(() => {
     // بعد از نشستن layout (فونت/تصویر) خطوط دوباره رسم شوند
     const t = setTimeout(() => setBump((b) => b + 1), 350);
@@ -144,31 +154,35 @@ export function QuoteDetail({ store, q }: QuoteDetailProps) {
   attachments.proformas.forEach((pf, i) => {
     if (!pf.id) return;
     attachParts.push(
-      <button
-        key={"pf" + i}
-        type="button"
-        className="detail-link"
-        title="دانلود پیش‌فاکتور"
-        onClick={() => api.files.download(q.id, "proforma", pf.id!, pf.name)}
-      >
-        <Paperclip className="me-1 inline h-3 w-3" />
-        پیش‌فاکتور: {pf.name}
-      </button>,
+      <span key={"pf" + i} className="inline-flex items-center">
+        <button
+          type="button"
+          className="detail-link"
+          title="مشاهده پیش‌فاکتور"
+          disabled={preview.loadingId === `proforma:${pf.id}`}
+          onClick={() => void preview.open(`proforma:${pf.id}`, pf.name)}
+        >
+          <Paperclip className="me-1 inline h-3 w-3" />
+          پیش‌فاکتور: {pf.name}
+        </button>
+      </span>,
     );
   });
   attachments.invoices.forEach((inv, i) => {
     if (!inv.id) return;
     attachParts.push(
-      <button
-        key={"inv" + i}
-        type="button"
-        className="detail-link"
-        title="دانلود فاکتور"
-        onClick={() => api.files.download(q.id, "invoice", inv.id!, inv.name)}
-      >
-        <Paperclip className="me-1 inline h-3 w-3" />
-        فاکتور اصلی: {inv.name}
-      </button>,
+      <span key={"inv" + i} className="inline-flex items-center">
+        <button
+          type="button"
+          className="detail-link"
+          title="مشاهده فاکتور"
+          disabled={preview.loadingId === `invoice:${inv.id}`}
+          onClick={() => void preview.open(`invoice:${inv.id}`, inv.name)}
+        >
+          <Paperclip className="me-1 inline h-3 w-3" />
+          فاکتور اصلی: {inv.name}
+        </button>
+      </span>,
     );
   });
 
@@ -251,6 +265,9 @@ export function QuoteDetail({ store, q }: QuoteDetailProps) {
           ))}
         </div>
       )}
+      {preview.item && (
+        <FilePreviewModal url={preview.item.url} name={preview.item.name} onClose={preview.close} />
+      )}
     </div>
   );
 }