Migrate to GA version of Realtime API, Upgrade AgentsSDK, and fix buffer bug

[bfioca-openai]

Summary

• Dependencies: Bumped @openai/agents to ^0.1.9 and openai to ^6.2.0 (plus transitives) so the app targets the GA realtime stack.
• Server: Replaced the deprecated /v1/realtime/sessions POST with openai.realtime.clientSecrets.create, supplying the GA session payload (model, audio formats, voice) and returning the expected shape.
• Client:
  • Send GA-compliant session.update payloads (type: "realtime") and adopt the new audio.* shape while listening for GA transcript events (response.output_audio_transcript.*).
  • Fixed push-to-talk drift by clearing the buffer on release and toggling mute on press/release; the same mute logic now covers PTT and playback-disable flows.
  • Emit structured audio format descriptors from audioFormatForCodec.
• Prompts: Switched all agent configs to the GA marin voice to match the updated transport.