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>

frontend/src/hooks/useStackActions.ts

@@ -20,6 +20,7 @@ export function useStackActions() {
       toast.success(`${label} ${id} ✓`, { id: t });
       qc.invalidateQueries({ queryKey: ["stacks"] });
       qc.invalidateQueries({ queryKey: ["stack", id] });
+      qc.invalidateQueries({ queryKey: ["stack-updates"] });
     } catch (err) {
       toast.error(apiErrorMessage(err), { id: t });
     } finally {