[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()
                 }
             }
         }

OSGKeyboard/Views/AppGroupErrorView.swift

@@ -0,0 +1,46 @@
+// AppGroupErrorView.swift
+// OSGKeyboard · Main App
+//
+// Shown in place of the normal Home/Onboarding flow when the App Group
+// container is not configured. The whole app is unusable without it (the
+// keyboard extension and the main app cannot share state), so we don't
+// try to be clever — we show a clear, actionable error and stop.
+//
+// We deliberately do NOT fatalError in release: the developer might be
+// running a TestFlight build with a stripped entitlement, and a friendly
+// screen is much better than a crash loop.
+
+import SwiftUI
+import OSGKeyboardShared
+
+struct AppGroupErrorView: View {
+    var body: some View {
+        VStack(spacing: Spacing.lg) {
+            Image(systemName: "exclamationmark.triangle.fill")
+                .font(.system(size: 48))
+                .foregroundStyle(Palette.danger)
+            Text("App Group 未配置")
+                .font(TypeStyle.title2)
+            Text("OSGKeyboard 需要 App Group 才能在键盘扩展和主 App 之间共享配置。")
+                .font(TypeStyle.body)
+                .multilineTextAlignment(.center)
+                .foregroundStyle(Palette.textSecondary)
+            VStack(alignment: .leading, spacing: Spacing.sm) {
+                Label("在 Apple Developer 后台创建 group.com.osgkeyboard.shared", systemImage: "1.circle")
+                Label("主 App 和键盘扩展都启用该 App Group", systemImage: "2.circle")
+                Label("重新生成 provisioning profile 并下载", systemImage: "3.circle")
+            }
+            .font(TypeStyle.body)
+            .foregroundStyle(Palette.textPrimary)
+        }
+        .padding(Spacing.lg)
+    }
+}
+
+#if DEBUG
+#Preview {
+    ThemedRoot {
+        AppGroupErrorView()
+    }
+}
+#endif