fix: refactor password reset dialog to its own StatefulWidget

Fixes red screen crash ('_dependents.isEmpty is not true') caused by
auth state change rebuilding the widget tree while the dialog was
still open and sharing the parent context across an async gap.

lib/main.dart

@@ -90,59 +90,13 @@ class _AuthGateState extends State<AuthGate> {
   /// Shows a dialog so the user can type a new password after clicking
   /// the "Reset Password" link from their email.
   Future<void> _showResetPasswordDialog() async {
-    final passwordController = TextEditingController();
+    if (!mounted) return;
 
     await showDialog<void>(
       context: context,
       barrierDismissible: false,
-      builder: (ctx) => AlertDialog(
-        title: const Text('Set New Password'),
-        content: TextField(
-          controller: passwordController,
-          obscureText: true,
-          decoration: const InputDecoration(
-            labelText: 'New password',
-            border: OutlineInputBorder(),
-          ),
-        ),
-        actions: [
-          TextButton(
-            onPressed: () => Navigator.of(ctx).pop(),
-            child: const Text('Cancel'),
-          ),
-          ElevatedButton(
-            onPressed: () async {
-              final newPassword = passwordController.text.trim();
-              if (newPassword.length < 6) {
-                ScaffoldMessenger.of(context).showSnackBar(
-                  const SnackBar(content: Text('Password must be at least 6 characters.')),
-                );
-                return;
-              }
-              try {
-                await supabase.auth.updateUser(
-                  UserAttributes(password: newPassword),
-                );
-                if (!ctx.mounted) return;
-                Navigator.of(ctx).pop();
-                if (!mounted) return;
-                ScaffoldMessenger.of(context).showSnackBar(
-                  const SnackBar(content: Text('Password updated successfully!')),
-                );
-              } on AuthException catch (e) {
-                if (!mounted) return;
-                ScaffoldMessenger.of(context).showSnackBar(
-                  SnackBar(content: Text(e.message), backgroundColor: Colors.red),
-                );
-              }
-            },
-            child: const Text('Save'),
-          ),
-        ],
-      ),
+      builder: (_) => const _ResetPasswordDialog(),
     );
-
-    passwordController.dispose();
   }
 
   @override
@@ -161,6 +115,86 @@ class _AuthGateState extends State<AuthGate> {
   }
 }
 
+// ── Reset Password Dialog ─────────────────────────────────────────────
+class _ResetPasswordDialog extends StatefulWidget {
+  const _ResetPasswordDialog();
+
+  @override
+  State<_ResetPasswordDialog> createState() => _ResetPasswordDialogState();
+}
+
+class _ResetPasswordDialogState extends State<_ResetPasswordDialog> {
+  final _passwordController = TextEditingController();
+  bool _isSaving = false;
+
+  @override
+  void dispose() {
+    _passwordController.dispose();
+    super.dispose();
+  }
+
+  Future<void> _save() async {
+    final newPassword = _passwordController.text.trim();
+    if (newPassword.length < 6) {
+      ScaffoldMessenger.of(context).showSnackBar(
+        const SnackBar(content: Text('Password must be at least 6 characters.')),
+      );
+      return;
+    }
+
+    setState(() => _isSaving = true);
+
+    try {
+      await supabase.auth.updateUser(
+        UserAttributes(password: newPassword),
+      );
+      if (!mounted) return;
+      Navigator.of(context).pop();
+      ScaffoldMessenger.of(context).showSnackBar(
+        const SnackBar(content: Text('Password updated successfully!')),
+      );
+    } on AuthException catch (e) {
+      if (!mounted) return;
+      setState(() => _isSaving = false);
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(content: Text(e.message), backgroundColor: Colors.red),
+      );
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return AlertDialog(
+      title: const Text('Set New Password'),
+      content: TextField(
+        controller: _passwordController,
+        obscureText: true,
+        decoration: const InputDecoration(
+          labelText: 'New password',
+          border: OutlineInputBorder(),
+        ),
+        onSubmitted: (_) => _save(),
+      ),
+      actions: [
+        TextButton(
+          onPressed: () => Navigator.of(context).pop(),
+          child: const Text('Cancel'),
+        ),
+        ElevatedButton(
+          onPressed: _isSaving ? null : _save,
+          child: _isSaving
+              ? const SizedBox(
+                  height: 18,
+                  width: 18,
+                  child: CircularProgressIndicator(strokeWidth: 2),
+                )
+              : const Text('Save'),
+        ),
+      ],
+    );
+  }
+}
+
 // ── Login Screen ──────────────────────────────────────────────────────
 class LoginScreen extends StatefulWidget {
   const LoginScreen({super.key});