feat: add message queue for sequential run processing (#501)

Allow sending multiple messages while a run is active. Messages are
queued on the server and processed sequentially after each run
completes. Each completed assistant message triggers speech playback
independently, and the UI shows queue status with a badge indicator.

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

packages/client/src/i18n/locales/en.ts

@@ -128,6 +128,8 @@ export default {
     inputPlaceholder: 'Type a message... (Enter to send, Shift+Enter for new line)',
     attachFiles: 'Attach files',
     autoPlaySpeech: 'Auto-play voice',
+    messageQueue: 'Message queue',
+    removeQueuedMessage: 'Remove queued message',
     stop: 'Stop',
     start: 'Start',
     stopGateway: 'Stop Gateway',