fix(conversation-assistant): Swift 6.2 compatibility

- Use .foregroundStyle(.tertiary) instead of .foregroundColor(.tertiary)
  to fix ShapeStyle vs Color type mismatch error
- Restore double-paren selector format Selector(("...")) to suppress
  warnings about private Objective-C selectors

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

features/conversation-assistant/macos/Sources/Views/MenuBarView.swift

@@ -39,7 +39,7 @@ struct MenuBarView: View {
 
                 Text(AppVersion.displayVersion)
                     .font(.caption2)
-                    .foregroundColor(.tertiary)
+                    .foregroundStyle(.tertiary)
 
                 Spacer()
 

features/conversation-assistant/macos/Sources/Views/MenuBarViewModel.swift

@@ -141,11 +141,11 @@ class MenuBarViewModel: ObservableObject {
         // Activate the app (required for menu bar apps to show settings)
         NSApp.activate(ignoringOtherApps: true)
         // Open settings window - macOS 14+ renamed to showSettingsWindow, older versions use showPreferencesWindow
-        // Note: Using string-based selector since #selector requires @objc exposure which NSApplication methods don't have
+        // Note: Using double-paren selector format to suppress warnings about private Objective-C selectors
         if #available(macOS 14, *) {
-            NSApp.sendAction(Selector("showSettingsWindow:"), to: nil, from: nil)
+            NSApp.sendAction(Selector(("showSettingsWindow:")), to: nil, from: nil)
         } else {
-            NSApp.sendAction(Selector("showPreferencesWindow:"), to: nil, from: nil)
+            NSApp.sendAction(Selector(("showPreferencesWindow:")), to: nil, from: nil)
         }
     }