Clear the stack update pill immediately after a manual/auto update (0.38.4)

The amber image-update indicator is fed from update_service._CACHE, which
only the background loop refreshed — after a per-stack Update/Pull the
stale digests kept the pill on until the next pass. Now the local digests
are reconciled with the cached remote digests right after a successful
pull/update (local backend, agent lifecycle, auto-update pass), and the
frontend invalidates the stack-updates queries after actions.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/services/auto_update_service.py

@@ -110,6 +110,7 @@ async def _run_local(session: Session, policy: AutoUpdate) -> None:
             _record(session, policy, "error", str(exc))
             await _safe_notify(EVENT_PULL_FAILED, f"Auto-update of '{stack_id}' failed", str(exc), session)
             return
+        update_service.refresh_stack_local(stack_id)
         _record(session, policy, "updated", stale)
         await _safe_notify(
             EVENT_STACK_AUTO_UPDATED, f"Stack '{stack_id}' auto-updated",