Add abstract BaseTTSProvider class that implements common OpenAI-compatible
TTS logic using the OpenAI SDK with configurable baseURL. Includes synthesize(),
listVoices(), and isHealthy() methods. Create TTS provider factory that
dynamically registers Kokoro (default), Chatterbox (premium), and Piper
(fallback) providers based on configuration. Update SpeechModule to use
the factory for TTS_PROVIDERS injection token.
Also fixes lint error in speaches-stt.provider.ts (Array<T> -> T[]).
30 tests added (22 base provider + 8 factory), all passing.
Fixes#391
Jason Woltje
3ae9e53bcc