feat: Kontakt-Ordner mit Drag&Drop Baum (wie KI-Chat Sidebar)

- Backend: ContactFolder model (hierarchisch, parent_id, sort_order)
- Migration 0022: contact_folders Tabelle + folder_id FK auf contacts
- CRUD Routes: /api/v1/contact-folders (list, create, update, delete, reorder)
- Move Contact API: /api/v1/contact-folders/contacts/{id}/move
- folder_id Filter in contacts list API
- Frontend: ContactFolderTree mit Baum-Struktur, Drag&Drop, Kontext-Menü
- Kontakt-Personen-Icon statt Ordner-Symbol
- ContactList Items draggable (List/Table/Cards View)
- React Query Hooks für Folder CRUD + Move Contact
- Alle 266 Frontend-Tests passing

app/routes/contacts.py

@@ -29,17 +29,19 @@ async def list_contacts(
     page_size: int = Query(20, ge=1, le=100),
     search: str | None = Query(None),
     type: str | None = Query(None, pattern="^(company|person)$"),
+    folder_id: str | None = Query(None),
     sort_by: str = Query("displayname"),
     sort_order: str = Query("asc", pattern="^(asc|desc)$"),
     db: AsyncSession = Depends(get_db),
     current_user: dict = Depends(require_permission("contacts:read")),
 ):
-    """List contacts with pagination, FTS search, type filter, sorting."""
+    """List contacts with pagination, FTS search, type/folder filter, sorting."""
     tenant_id = uuid.UUID(current_user["tenant_id"])
     return await contact_service.list_contacts(
         db, tenant_id,
         page=page, page_size=page_size, search=search,
-        contact_type=type, sort_by=sort_by, sort_order=sort_order,
+        contact_type=type, folder_id=folder_id,
+        sort_by=sort_by, sort_order=sort_order,
         resolved_perms=current_user,
     )