Add Google realtime voice options

[rogerchappel]

Summary

• add Google as a selectable realtime voice provider in shared voice metadata
• expose Google realtime voices from the voice list endpoint so they appear under the Realtime filter
• map selected Google realtime voices to OpenClaw realtime session provider/voice/model overrides

Verification

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

Risk

Medium: expands voice provider metadata to include Google. Normal TTS fallback remains unchanged because Google is not treated as an explicit server TTS provider in CrewCMD.