feat: sync force-quit Flow teardown and polish macOS local ASR UX

End Live Activities and release the audio session synchronously on
applicationWillTerminate, and continue macOS local-model install,
onboarding, and settings polish on this branch.

OSGKeyboard/Services/AppURLHandler.swift

@@ -59,6 +59,14 @@ final class AppURLHandler: NSObject, UIApplicationDelegate {
         configuration.delegateClass = AppSceneDelegate.self
         return configuration
     }
+
+    /// 后台音频会话仍 running 时，用户强杀常会进入此回调（约 5 秒清理窗口）。
+    /// 同步释放麦克风 + 结束 Live Activity，避免重开后「麦克风被占用」。
+    func applicationWillTerminate(_ application: UIApplication) {
+        MainActor.assumeIsolated {
+            FlowTerminationCoordinator.performSynchronousTerminationCleanup()
+        }
+    }
 }
 
 final class AppSceneDelegate: NSObject, UIWindowSceneDelegate {

OSGKeyboard/Services/FlowLiveActivityController.swift

@@ -116,4 +116,21 @@ enum FlowLiveActivityController {
             }
         }
     }
+
+    /// `applicationWillTerminate` 专用：阻塞到所有 `end` 完成，避免进程先退出而锁屏卡片残留。
+    nonisolated static func endAllSynchronouslyOnTerminate() {
+        let semaphore = DispatchSemaphore(value: 0)
+        Task.detached(priority: .userInitiated) {
+            let activities = Activity<FlowActivityAttributes>.activities
+            let count = activities.count
+            for activity in activities {
+                await activity.end(activity.content, dismissalPolicy: .immediate)
+            }
+            FlowDiagnostics.log("Live Activity ended synchronously on terminate (count=\(count))")
+            semaphore.signal()
+        }
+        semaphore.wait()
+        currentPhase = .idle
+        currentActivity = nil
+    }
 }

OSGKeyboard/Services/FlowSessionManager.swift

@@ -88,6 +88,7 @@ final class FlowSessionManager: ObservableObject {
         capture.onEngineLiveChanged = { [weak self] _ in
             self?.refreshHostReady()
         }
+        FlowTerminationCoordinator.register(self)
     }
 
     // MARK: - Public
@@ -210,6 +211,73 @@ final class FlowSessionManager: ObservableObject {
         AppPermissions.openSystemSettings()
     }
 
+    /// 强杀专用同步 teardown：不等待 ASR/LLM；Live Activity 由
+    /// `FlowTerminationCoordinator` 同步 `end`。
+    func prepareForProcessTermination() {
+        debug("prepareForProcessTermination")
+
+        coldStartContext = nil
+        isColdStartHandoff = false
+        coldStartRecoveryTask?.cancel()
+        coldStartRecoveryTask = nil
+        startTask?.cancel()
+        startTask = nil
+        commandObserver = nil
+        pollingTask?.cancel()
+        pollingTask = nil
+        heartbeatTask?.cancel()
+        heartbeatTask = nil
+        expiryTask?.cancel()
+        expiryTask = nil
+        levelTask?.cancel()
+        levelTask = nil
+        finalizeTask?.cancel()
+        finalizeTask = nil
+        utteranceSafetyTask?.cancel()
+        utteranceSafetyTask = nil
+        asrTask?.cancel()
+        asrTask = nil
+        chunkedPipeline = nil
+
+        if isUtteranceRecording || isUtteranceProcessing {
+            capture.cancelUtterance()
+            asr.cancel()
+        }
+
+        capture.cancelUtterance()
+        if capture.running {
+            capture.stop()
+        }
+
+        endBackgroundKeepAlive()
+        ScreenWakeLock.release()
+
+        sessionASR?.cancel()
+        sessionASR = nil
+        sessionASREngineMode = nil
+        sessionASRWarmedLocaleID = nil
+
+        if isActive || FlowSessionBridge.isSessionActive() {
+            FlowSessionBridge.markSessionInactive()
+            FlowSessionDarwin.postSessionChanged()
+        }
+
+        activeSessionId = nil
+        currentUtteranceId = nil
+        currentCommandSeq = 0
+        lastHandledCommandSeq = 0
+        isUtteranceRecording = false
+        isUtteranceProcessing = false
+        isActive = false
+        isStarting = false
+        sessionExpiresAt = nil
+        sessionWarning = nil
+        currentPartial = ""
+        lastFinal = ""
+        chunkWarnings = []
+        FlowSessionBridge.setHostReady(false)
+    }
+
     func endSession() {
         guard isActive else { return }
         debug("Flow session ended")

OSGKeyboard/Services/FlowTerminationCoordinator.swift

@@ -0,0 +1,24 @@
+// FlowTerminationCoordinator.swift
+// OSGKeyboard · Main App
+//
+// 桥接 `UIApplicationDelegate.applicationWillTerminate` 与 `FlowSessionManager`。
+// SwiftUI 里 `FlowSessionManager` 是 `@StateObject`，AppDelegate 无法直接持有；
+// 此处用弱引用在进程退出窗口（约 5 秒）内同步释放麦克风与 Live Activity。
+
+import Foundation
+
+@MainActor
+enum FlowTerminationCoordinator {
+    private static weak var sessionManager: FlowSessionManager?
+
+    /// `FlowSessionManager.init()` 注册当前实例。
+    static func register(_ manager: FlowSessionManager) {
+        sessionManager = manager
+    }
+
+    /// 强杀 / 系统终止时调用。必须在主线程执行（`applicationWillTerminate` 保证）。
+    static func performSynchronousTerminationCleanup() {
+        sessionManager?.prepareForProcessTermination()
+        FlowLiveActivityController.endAllSynchronouslyOnTerminate()
+    }
+}