- Export splitSentences() with title-abbreviation protection (Dr., Mr. etc.)
- Add synthesizeSentenceStream() AsyncGenerator yielding per-sentence audio chunks
- Add synthesizeMultiLang() synthesizing same text in N voices via Promise.all
- Add POST /api/synthesize/stream SSE endpoint with base64 audio per sentence
- Add POST /api/synthesize/multi-lang returning array of voiceId+audio pairs
- Existing POST /api/synthesize unchanged (backward compatible)