Enqueue Drive sync as a Django task and return 202 (#57).

Sync now / webhooks / cron share enqueue_drive_sync so HTTP no longer
blocks on Drive list/ingest. ImmediateBackend still runs in-process via
a background thread; status and errors stay on the connection for FE poll.

README.md

@@ -235,7 +235,7 @@ true for Founders/Pro/Business/Backer, false for Standard by default).
 | `GET /api/drive/connections/` | Caller's personal connections + their company's company connections |
 | `DELETE /api/drive/connections/<id>/` | Disconnect (owner for personal, company manager for company) — deactivates + clears tokens, keeps history |
 | `POST /api/drive/connections/<id>/resources/` | `{ "resource_ids": [...], "resource_labels": [...] }` — folder/shared-drive/site ids to sync; empty = provider root |
-| `POST /api/drive/connections/<id>/sync/` | Sync now (`chat_backend/services/drive_sync.py::sync_connection`) |
+| `POST /api/drive/connections/<id>/sync/` | Enqueue sync now (`chat_backend/drive_tasks.py`) — returns **202** with `connection.last_sync_status=pending`; poll `GET /api/drive/connections/` for `ok` / `error` + `last_sync_error` |
 
 **Provider scope differences:**
 - Google: same `drive.readonly` scope for personal and company; company sync
@@ -243,10 +243,12 @@ true for Founders/Pro/Business/Backer, false for Standard by default).
 - Microsoft: personal uses `Files.Read`; company uses `Files.Read.All
   Sites.Read.All` and syncs SharePoint sites (`selected_resource_ids` = site ids).
 
-**Workers / webhooks (#52):**
-- `python manage.py sync_drive_connections [--connection-id N]` — cron/worker entry point.
+**Workers / webhooks (#52, #57):**
+- `python manage.py sync_drive_connections [--connection-id N]` — enqueue sync tasks (default).
+- `python manage.py sync_drive_connections --sync-now` — run sync inline in this process (cron/debug).
+- Django 6 `TASKS` (see `settings.py`): default `ImmediateBackend` runs tasks in-process; Sync now still returns 202 by dispatching on a background thread. Swap `TASKS` to a durable queue + worker for production scale.
 - `POST /api/drive/webhooks/google/` / `POST /api/drive/webhooks/microsoft/` —
-  provider push-notification stubs (`AllowAny`); acknowledge `200` and call
+  provider push-notification stubs (`AllowAny`); acknowledge `200` and enqueue
   `sync_connection` when the notification's `connection_id` is resolvable,
   else just `200` (no-op). Microsoft's subscription-creation `validationToken`
   handshake is echoed back as `text/plain`.