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_model.dart

@@ -0,0 +1,26 @@
+import 'package:flutter/widgets.dart';
+
+/// Stub ViewModel for the overlay feature.
+///
+/// [Overlay] has been a major problem and is deferred. This stub
+/// reserves the abstraction point for future implementation.
+///
+/// The original [OverlayProvider] mixed overlay IPC, GPS forwarding,
+/// timers, and app foreground management — all of which violated
+/// separation of concerns.
+@Deprecated('Overlay is deferred. This stub reserves the abstraction point.')
+class OverlayViewModel extends ChangeNotifier {
+  bool get isOverlayActive => false;
+
+  void init() {
+    // No-op — overlay is deferred
+  }
+
+  void toggleOverlay() {
+    // No-op — overlay is deferred
+  }
+
+  void closeOverlay() {
+    // No-op — overlay is deferred
+  }
+}