fix(quotes): derive decision.project_id from accept item_projects

Multi-project quotes: the manager picks one project per line item in the
accept modal (item_projects), but accept_quote only auto-filled
decision.project_id from existing line_item_projects (≤1). For items
without a single existing line-project the decision stayed NULL, so
/ pm/on-the-way (filtered by ItemDecision.project_id) never showed those
items to any project manager — they accumulated only in the global admin
list. Now derivation order is: explicit decision.project_id →
payload.item_projects (single) → existing line_item_projects (single) →
NULL (office-only, never misattributed). Verified E2E: two items of one
quote accepted to two projects appear in exactly their own PM's
on-the-way.

backend/app/services/quote_service.py

@@ -416,6 +416,9 @@ async def accept_quote(db: AsyncSession, quote_id: UUID, payload: AcceptQuoteIn,
 
         # --- process item decisions (UPSERT) ---
         chosen_ts_ids: set[UUID] = set()
+        # پروژه‌های ارسالی در payload.item_projects — منبع اصلی برای
+        # decision.project_id (مدیر تدارکات برای هر قلم یک پروژه انتخاب می‌کند)
+        proj_by_line: dict[UUID, list[UUID]] = {e.line_item_id: list(e.project_ids) for e in payload.item_projects}
         for decision_in in payload.item_decisions:
             decision = await db.scalar(
                 select(ItemDecision).where(ItemDecision.line_item_id == decision_in.line_item_id).with_for_update()
@@ -460,10 +463,19 @@ async def accept_quote(db: AsyncSession, quote_id: UUID, payload: AcceptQuoteIn,
                 decision.adjusted_unit_price = decision_in.adjusted_unit_price
                 decision.adjusted_notes = decision_in.adjusted_notes
                 decision.decided_at = utcnow()
-                # v2.6: the SINGLE purchased project (proc manager picks it;
-                # auto-filled when the offer had exactly one project).
+                # v2.6: the SINGLE purchased project (proc manager picks it).
+                # Derivation order:
+                #   1) explicit decision_in.project_id
+                #   2) payload.item_projects for this line item (exactly one)
+                #   3) existing line_item_projects (exactly one)
+                # otherwise NULL — the item stays visible only to the office
+                # until a project is assigned (never wrongly visible to a PM).
                 if decision_in.project_id is not None:
                     decision.project_id = decision_in.project_id
+                else:
+                    accept_projs = proj_by_line.get(decision_in.line_item_id) or []
+                    if len(accept_projs) == 1:
+                        decision.project_id = accept_projs[0]
                     else:
                         line_projs = (
                             (await db.execute(