feat: TypeWhisper Flow sessions, Phase 4 UX, and GitHub Pages privacy site

Migrate keyboard dictation to continuous Flow sessions with auto-start,
tap-to-toggle recording, 60s countdown, five-step onboarding, and App Group
IPC. Add docs/ GitHub Pages site with en/zh privacy policy for App Store compliance.

OSGKeyboardShared/Services/AppGroupStore.swift

@@ -14,8 +14,15 @@ import Foundation
 public struct AppGroupStore: @unchecked Sendable {
     public let defaults: UserDefaults
 
-    public init(defaults: UserDefaults = AppGroup.defaults) {
-        self.defaults = defaults
+    public init(defaults: UserDefaults? = nil) {
+        if let defaults {
+            self.defaults = defaults
+            return
+        }
+        // Never hard-crash on implicit construction sites (e.g. default
+        // service initializers). If App Group is unavailable, use .standard
+        // so callers can still surface a user-facing setup error.
+        self.defaults = AppGroup.isAvailable ? AppGroup.defaults : .standard
     }
 
     // MARK: - Keys