move menu styling to theme for app-wide consistency

Add menuTheme and menuButtonTheme to ThemeData matching the existing
overlay surface style (12px radius, outline border, compact density).
Remove per-use styling from chat_tabs.dart.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/screens/channel/chat/widgets/chat_tabs.dart

@@ -262,26 +262,11 @@ class ChatTabs extends StatelessWidget {
       );
     }
 
-    final borderColor =
-        Theme.of(context).colorScheme.outlineVariant.withValues(alpha: 0.5);
-
     return MenuAnchor(
-      style: MenuStyle(
-        padding: const WidgetStatePropertyAll(EdgeInsets.symmetric(vertical: 4)),
-        shape: WidgetStatePropertyAll(
-          RoundedRectangleBorder(
-            borderRadius: BorderRadius.circular(12),
-            side: BorderSide(color: borderColor),
-          ),
-        ),
-      ),
       menuChildren: [
         if (isActivated)
           MenuItemButton(
             leadingIcon: const Icon(Icons.power_off_rounded, size: 18),
-            style: MenuItemButton.styleFrom(
-              visualDensity: VisualDensity.compact,
-            ),
             child: const Text('Disconnect'),
             onPressed: () {
               HapticFeedback.lightImpact();
@@ -294,9 +279,6 @@ class ChatTabs extends StatelessWidget {
             size: 18,
             color: Theme.of(context).colorScheme.error,
           ),
-          style: MenuItemButton.styleFrom(
-            visualDensity: VisualDensity.compact,
-          ),
           child: Text(
             'Remove',
             style: TextStyle(color: Theme.of(context).colorScheme.error),

lib/theme.dart

@@ -136,6 +136,24 @@ class FrostyThemes {
         backgroundColor: backgroundColor,
         surfaceTintColor: backgroundColor,
       ),
+      menuTheme: MenuThemeData(
+        style: MenuStyle(
+          padding: const WidgetStatePropertyAll(
+            EdgeInsets.symmetric(vertical: 4),
+          ),
+          shape: WidgetStatePropertyAll(
+            RoundedRectangleBorder(
+              borderRadius: const BorderRadius.all(Radius.circular(12)),
+              side: BorderSide(color: borderColor),
+            ),
+          ),
+        ),
+      ),
+      menuButtonTheme: MenuButtonThemeData(
+        style: MenuItemButton.styleFrom(
+          visualDensity: VisualDensity.compact,
+        ),
+      ),
       dialogTheme: DialogThemeData(
         backgroundColor: backgroundColor,
         surfaceTintColor: backgroundColor,