feat(overlay): create stub ViewModel and View for deferred overlay feature

- Stub OverlayViewModel reserves abstraction point
- Stub OverlayView shows 'Overlay deferred' placeholder
- Original OverlayProvider (274 lines) was too tangled:
  mixed IPC, GPS forwarding, timers, foreground mgmt
- Will be reimplemented properly when overlay issues are resolved

lib/ui/features/overlay/overlay_view.dart

@@ -0,0 +1,17 @@
+import 'package:flutter/material.dart';
+
+/// Stub view for the overlay feature.
+///
+/// [Overlay] has been deferred due to ongoing issues. This placeholder
+/// reserves the UI layer for when the overlay is properly reimplemented
+/// with the new architecture.
+class OverlayView extends StatelessWidget {
+  const OverlayView({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return const Center(
+      child: Text('Overlay deferred'),
+    );
+  }
+}