feat: add Chatterbox TTS engine for multilingual voice cloning

- New ChatterboxTTSBackend wrapping ChatterboxMultilingualTTS (ResembleAI/chatterbox)
- Supports 23 languages including Hebrew, forces CPU on macOS (MPS issue)
- Monkey-patches torch.load for CPU loading, forces eager attention for compatibility
- trim_tts_output utility cuts trailing silence/hallucination from Chatterbox output
- Full engine integration: /generate, /generate/stream, model status/download/delete
- Hebrew (he) added to supported languages in frontend and backend validation
- Single flat model dropdown extended with Chatterbox option in both generation UIs
- ModelManagement UI groups LuxTTS and Chatterbox under 'Other Voice Models' section

backend/backends/__init__.py

@@ -121,6 +121,7 @@ _stt_backend: Optional[STTBackend] = None
 TTS_ENGINES = {
     "qwen": "Qwen TTS",
     "luxtts": "LuxTTS",
+    "chatterbox": "Chatterbox TTS",
 }
 
 
@@ -167,6 +168,9 @@ def get_tts_backend_for_engine(engine: str) -> TTSBackend:
         elif engine == "luxtts":
             from .luxtts_backend import LuxTTSBackend
             backend = LuxTTSBackend()
+        elif engine == "chatterbox":
+            from .chatterbox_backend import ChatterboxTTSBackend
+            backend = ChatterboxTTSBackend()
         else:
             raise ValueError(f"Unknown TTS engine: {engine}. Supported: {list(TTS_ENGINES.keys())}")