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.

OSGKeyboardExt/Utilities/ExtL10n.swift

@@ -0,0 +1,17 @@
+// ExtL10n.swift
+// OSGKeyboard · Keyboard Extension
+//
+// Loads strings from the extension bundle. Replaces the old KeyboardL10n
+// hard-coded fallback map — keys live in Localizable.strings.
+
+import Foundation
+
+enum ExtL10n {
+    static func string(_ key: String) -> String {
+        NSLocalizedString(key, bundle: .main, comment: "")
+    }
+
+    static func format(_ key: String, _ args: CVarArg...) -> String {
+        String(format: string(key), locale: Locale.current, arguments: args)
+    }
+}