[codex] Add Twilio ConversationRelay voice channel

[furukama]

Summary

• add a new voice channel powered by Twilio ConversationRelay, including webhook handling, websocket relay parsing, per-call session lifecycle, and Twilio request validation
• wire voice into gateway startup, shutdown, status reporting, session/channel inference, and runtime config/secret resolution
• cover the new behavior with unit and gateway tests, including custom webhook path routing and shared-secret-backed Twilio auth token handling

Why

HybridClaw did not have a voice channel implementation. This adds an inbound Twilio voice path that fits the existing text-channel gateway model while keeping Twilio-specific transport handling isolated under src/channels/voice/.

Impact

Users can enable a Twilio-backed voice channel through runtime config and handle live phone conversations through the existing gateway pipeline. The gateway also exposes clearer voice status and respects secret-backed Twilio credentials and configurable voice webhook paths.

Root Cause

There was no native voice transport, and the follow-up review fixes addressed two boundary issues discovered during implementation: voice route dispatch was hard-coded to /voice, and startup/signature validation bypassed the shared resolved Twilio auth token path.

Validation

• npm run typecheck
• npm run lint
• npx vitest run --configLoader runner --config vitest.unit.config.ts tests/gateway-main.test.ts tests/gateway-http-server.test.ts tests/runtime-config.secret-refs.test.ts tests/voice.webhook.test.ts tests/voice.security.test.ts tests/voice.conversation-relay.test.ts tests/voice.runtime.test.ts
• npx vitest run --configLoader runner --config vitest.unit.config.ts tests/channel-registry.test.ts tests/session-reset.test.ts tests/runtime-config.secret-refs.test.ts tests/voice.webhook.test.ts tests/voice.security.test.ts tests/voice.conversation-relay.test.ts tests/gateway-main.test.ts tests/gateway-status.test.ts