feat(flow): harden host handoff, session UX, and Live Activity brand

- fix(keyboard): drop unusable extensionContext.open; report the real
  result of UIApplication.open and cancel the start watchdog immediately
  on failure with clear "open OSGKeyboard" guidance instead of a 30s spin
- feat(capture): recover from audio route changes (AirPods/wired headset
  plug-unplug) and phone-call interruptions by rebuilding the engine/tap
  against the live hardware format
- feat(home): add a "Start" button in the Home footer when a session is
  inactive and permissions are granted (no-jump manual restart)
- feat(hostapps): expand the return whitelist to 46 apps (Signal, Zoom,
  Instagram, X, Douyin, Zhihu, Bilibili, Things, Firefox, ...) with
  en/zh-Hans names and synced LSApplicationQueriesSchemes
- feat(island): use a "ready" checkmark instead of a mic glyph while idle
  and set a staleDate so an orphaned Live Activity fades after a force-quit
- feat(coldstart): use the template OSG brand mark instead of a system
  waveform glyph in the cold-start overlay
- perf(keyboard): rely on Darwin notifications as the primary session
  signal and drop the fallback poll from 1s to 3s
- fix(keyboard): remove the redundant "Start" text button next to the
  inactive-session hint on the keyboard
- docs: correct the per-take cap to 210s (3.5 min) and document that
  force-quitting no longer resurrects the session (tracker + READMEs)

OSGKeyboardExt/Services/KeyboardFlowCoordinator.swift

@@ -61,12 +61,18 @@ final class KeyboardFlowCoordinator {
         isPendingFlowStart || isFlowRecording || isAwaitingFlowResult
     }
 
+    /// Session/transcription changes are pushed in real time by Darwin
+    /// notifications (see `KeyboardConfigSync.installDarwinObservers`), so this
+    /// loop is only a low-frequency safety net for coalesced/dropped Darwin
+    /// signals — hence 3 s rather than 1 Hz to save battery while idle.
+    private static let sessionMonitorIntervalNs: UInt64 = 3_000_000_000
+
     func startSessionMonitor() {
         flowSessionMonitorTask?.cancel()
         flowSessionMonitorTask = Task { @MainActor [weak self] in
             while !Task.isCancelled {
                 self?.refreshSessionState()
-                try? await Task.sleep(nanoseconds: 1_000_000_000)
+                try? await Task.sleep(nanoseconds: Self.sessionMonitorIntervalNs)
             }
         }
     }
@@ -168,8 +174,14 @@ final class KeyboardFlowCoordinator {
         debug("openHostApp path=\(path) success=\(success)")
         guard !success else { return }
 
+        // The open genuinely failed (iOS blocked it / no Full Access). Don't
+        // let the 30s watchdog spin — cancel the pending start immediately and
+        // guide the user to open OSGKeyboard manually.
         if path == "startflow", isPendingFlowStart {
-            state.lastTranscript = ExtL10n.string("keyboard.flow.manualOpenHost")
+            isPendingFlowStart = false
+            flowStartDeadline = 0
+            stopFlowWatchdog()
+            showManualOpenHint(path: "startflow")
             return
         }