Apply selected voice settings to realtime voice

[rogerchappel]

Summary

• pass the resolved chat/agent voice settings into VoiceAgent realtime startup
• map OpenAI voice selections to OpenClaw realtime session provider/voice/model overrides
• avoid forwarding non-realtime TTS providers or incompatible TTS-only OpenAI voices into realtime sessions

Verification

• pnpm test -- src/lib/realtime-voice-client.test.ts
• pnpm typecheck
• git diff --check
• pre-push: pnpm typecheck && pnpm build

Risk

Medium: changes realtime session startup parameters, but defaults remain unchanged unless an OpenAI voice is explicitly selected.