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/HostAppLauncher.swift

@@ -1,9 +1,18 @@
 // HostAppLauncher.swift
 // OSGKeyboard · Keyboard Extension
 //
-// Opens the host app via URL using extension-safe strategies:
-// 1. `extensionContext.open` (official)
-// 2. Responder-chain `UIApplication.open` (TypeWhisper pattern)
+// Opens the host app from the keyboard extension.
+//
+// Reality check (verified against iOS 18–26 behaviour):
+//   • `extensionContext.open` is documented for Today widgets only; for a
+//     keyboard extension it resolves `false`, so we do not use it.
+//   • The deprecated `openURL:` selector hack was disabled in iOS 18
+//     ("BUG IN CLIENT OF UIKIT … migrate to open(_:options:completionHandler:)").
+//   • The still-working path is: walk the responder chain to `UIApplication`
+//     and call the non-deprecated `open(_:options:completionHandler:)`. This
+//     requires Full Access and grows less reliable on newer iOS, so we report
+//     the *real* success from the completion handler instead of assuming it
+//     worked — callers degrade to on-keyboard guidance when it returns false.
 
 import UIKit
 
@@ -14,34 +23,17 @@ enum HostAppLauncher {
         from controller: KeyboardViewController,
         completion: @escaping @MainActor (Bool) -> Void
     ) {
-        if let context = controller.extensionContext {
-            context.open(url) { success in
-                Task { @MainActor in
-                    if success {
-                        completion(true)
-                        return
-                    }
-                    completion(openViaResponderChain(url, from: controller))
-                }
-            }
-            return
-        }
-        completion(openViaResponderChain(url, from: controller))
-    }
-
-    @MainActor
-    private static func openViaResponderChain(
-        _ url: URL,
-        from controller: KeyboardViewController
-    ) -> Bool {
         var responder: UIResponder? = controller
         while let current = responder {
             if let application = current as? UIApplication {
-                application.open(url, options: [:]) { _ in }
-                return true
+                application.open(url, options: [:]) { success in
+                    Task { @MainActor in completion(success) }
+                }
+                return
             }
             responder = current.next
         }
-        return false
+        // No `UIApplication` in the responder chain — cannot open the host app.
+        completion(false)
     }
 }