feat(speech): add prompt voice input (#249)

## Summary
- add server-backed speech capabilities and transcription endpoints plus
UI settings for speech configuration
- add push-to-talk prompt voice input with microphone controls,
transcription insertion, and browser capability gating
- keep prompt controls aligned by restoring right-side nav placement and
moving the mic beside the expand control

packages/ui/src/lib/i18n/messages/en/messaging.ts

@@ -138,4 +138,11 @@ export const messagingMessages = {
   "promptInput.send.ariaLabel": "Send message",
   "promptInput.send.errorFallback": "Failed to send message",
   "promptInput.send.errorTitle": "Send failed",
+  "promptInput.voiceInput.start.title": "Start voice input",
+  "promptInput.voiceInput.stop.title": "Stop recording and transcribe",
+  "promptInput.voiceInput.transcribing.title": "Transcribing audio",
+  "promptInput.voiceInput.error.title": "Voice input failed",
+  "promptInput.voiceInput.error.permission": "Microphone access is required to record voice input.",
+  "promptInput.voiceInput.error.unsupported": "Voice input is not supported in this browser.",
+  "promptInput.voiceInput.error.transcribe": "Unable to transcribe the recorded audio.",
 } as const