Fixes#2820
The `speak()` method returns `{ success: false, error }` instead of throwing
on failure. Two call sites were not checking this return value, causing TTS
errors to be silently swallowed:
1. `handleInboundResponse()` in webhook.ts - callers never received AI response audio
2. `continueCall()` in manager.ts - continued to "listening" state even when TTS failed
Changes:
- webhook.ts: Check `speak()` return value and log errors
- manager.ts: Check `speak()` return value in `continueCall()` and return early on failure
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
3ce5ac922e