add native picker and error dialog to project switcher

The project switcher dropdown's "Open Local Project" action now uses
the native directory picker (same as the welcome screen). Shows "No
git repo found" dialog when the selected directory is not a git
repository.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/app.dart

@@ -286,15 +286,7 @@ class _LeftHatContent extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     if (kIsWeb) return const SizedBox.shrink();
-    if (!kIsWeb && Platform.isMacOS) {
-      return Row(children: [
-        _TrafficDot(color: const Color(0xFFFF5F57), onTap: wc.close),
-        const SizedBox(width: 6),
-        _TrafficDot(color: const Color(0xFFFEBC2E), onTap: wc.minimize),
-        const SizedBox(width: 6),
-        _TrafficDot(color: const Color(0xFF28C840), onTap: wc.toggleMaximize),
-      ]);
-    }
+    // On macOS the native titlebar draws traffic lights; skip duplicates.
     return const SizedBox.shrink();
   }
 }
@@ -432,8 +424,27 @@ class _ProjectSwitcherDropdownState extends State<_ProjectSwitcherDropdown> {
     widget.onDismiss();
   }
 
-  void _openFolder() {
+  void _openFolder() async {
     widget.onDismiss();
+
+    try {
+      final picked = await widget.kernel.window.pickDirectory();
+      if (picked != null) {
+        final ok = await widget.kernel.project.open(picked);
+        if (ok) {
+          widget.kernel.panels.activateTab(Slots.workspace, 'claude.primary');
+        } else {
+          widget.kernel.dialog.show((ctx, dismiss) => _NotARepoDialog(
+            path: picked,
+            onDismiss: () => dismiss(),
+          ));
+        }
+      }
+      return;
+    } on MissingPluginException {
+      // Fall through to text dialog.
+    }
+
     widget.kernel.dialog.show<String>((ctx, dismiss) {
       return _OpenFolderDialog(
         onOpen: (path) async {
@@ -681,6 +692,48 @@ class _OpenFolderDialogState extends State<_OpenFolderDialog> {
   }
 }
 
+class _NotARepoDialog extends StatelessWidget {
+  const _NotARepoDialog({required this.path, required this.onDismiss});
+  final String path;
+  final VoidCallback onDismiss;
+
+  @override
+  Widget build(BuildContext context) {
+    final tokens = ClideTheme.of(context).surface;
+    return Container(
+      width: 420,
+      padding: const EdgeInsets.all(20),
+      decoration: BoxDecoration(
+        color: tokens.modalSurfaceBackground,
+        border: Border.all(color: tokens.modalSurfaceBorder),
+        borderRadius: BorderRadius.circular(6),
+      ),
+      child: Column(
+        mainAxisSize: MainAxisSize.min,
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: [
+          const ClideText('No git repo found', fontSize: 16, fontWeight: FontWeight.w600),
+          const SizedBox(height: 8),
+          ClideText(path, muted: true, fontSize: 13),
+          const SizedBox(height: 8),
+          const ClideText(
+            'A clide project root requires a git repository.',
+            muted: true,
+            fontSize: 13,
+          ),
+          const SizedBox(height: 16),
+          Row(
+            mainAxisAlignment: MainAxisAlignment.end,
+            children: [
+              ClideButton(label: 'OK', onPressed: () => onDismiss()),
+            ],
+          ),
+        ],
+      ),
+    );
+  }
+}
+
 class SlotHost extends StatelessWidget {
   const SlotHost({super.key, required this.slot});
   final SlotId slot;