feat: complete Phase 4 batch F, keyboard i18n, and Pages app icon

Remove KeyboardL10n hard-coded fallbacks in favor of ExtL10n and extension
Localizable.strings. Add Flow session expiry hints, Darwin cross-process
notifications, session monitor on the keyboard, and app icon on GitHub Pages.

OSGKeyboardShared/Services/KeyboardState.swift

@@ -69,6 +69,8 @@ public final class KeyboardState: ObservableObject {
     @Published public var onDeviceSupported: Bool = false
     /// Seconds remaining in the current utterance (Flow tap-to-talk).
     @Published public var utteranceRemainingSeconds: Int = Int(FlowSessionKeys.maxUtteranceDuration)
+    /// Whether the host app's Flow voice session is currently valid.
+    @Published public var flowSessionActive: Bool = false
     /// "local" → ASR only, no LLM. "cloud" → ASR + optional LLM polish.
     @Published public var engineMode: String = "cloud"