[JJC-20260618-005-B] Fix 6 critical bugs from review

- BUG-1: Restore KeyboardRootView top highlight + divider
- BUG-2: App Group unavailable -> friendly error view (no fatalError)
- BUG-3: pressBegan race condition (sync phase to .requestingPermissions)
- BUG-4: cancelled LLMError no longer re-inserts original text
- BUG-6: mode switch during recording flushes partial
- ARCH-A1: State.Phase add .requestingPermissions + .denied(Reason)

Notes:
- 8/8 tests pass (LLMClientTests)
- BUILD SUCCEEDED for both OSGKeyboard and OSGKeyboardExt
- New file AppGroupErrorView.swift auto-registered via XcodeGen
- Info.plist left untouched (NSSpeechRecognitionUsageDescription kept from A block)

OSGKeyboard/OSGKeyboardApp.swift

@@ -11,12 +11,14 @@ struct OSGKeyboardApp: App {
     var body: some Scene {
         WindowGroup {
             ThemedRoot {
-                Group {
+                if AppGroup.isAvailable {
                     if config.isConfigured {
                         HomeView()
                     } else {
                         OnboardingView(config: config)
                     }
+                } else {
+                    AppGroupErrorView()
                 }
             }
         }