Add sidebar app sub-nav with categories, category filter, and re-analysis on category creation

- Sidebar: Apps accordion expands to Documents, which expands to list all
  user categories; clicking a category navigates to /apps/documents?category_id=<id>
- DocumentsPage: reads category_id from URL and applies filter; shows active
  category chip in FilterBar with dismiss; removed TagEditor (deferred)
- doc-service GET /documents: new category_id query param filters via subquery
- doc-service POST /documents/categories: detects similar category names and
  triggers background re-analysis of affected documents so the new category
  surfaces as a pending AI suggestion on relevant docs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

features/doc-service/app/routers/documents.py

@@ -175,6 +175,7 @@ async def list_documents(
     status: str | None = Query(default=None),
     document_type: str | None = Query(default=None),
     search: str | None = Query(default=None),
+    category_id: str | None = Query(default=None),
     user_id: str = Depends(get_user_id),
     db: AsyncSession = Depends(get_db),
 ) -> DocumentPage:
@@ -197,6 +198,11 @@ async def list_documents(
                 Document.document_type.ilike(like),
             )
         )
+    if category_id:
+        subq = select(CategoryAssignment.document_id).where(
+            CategoryAssignment.category_id == category_id
+        )
+        conditions.append(Document.id.in_(subq))
 
     count_result = await db.execute(
         select(func.count(Document.id)).where(*conditions)