feat: Add OpenAI-compatible TTS endpoint and engines

- Implements POST /v1/audio/speech endpoint (OpenAI API compatible).
- Integrates Kokoro and XTTS engines (including dependencies and implementations).
- Updates main application to register new engines and router.
- Adds unit tests for OpenAI compatibility.
- Updates requirements.txt for new engines.

app/config.py

@@ -19,11 +19,22 @@ class Settings(BaseSettings):
     ACTIVE_ENGINES: Set[str] = {"piper"}
     ASSET_DIR: str = "app/asset"
     AUDIO_CACHE_DIR: str = "app/asset/audio"
+    MODELS_DIR: str = "app/models"
+    LOG_LEVEL: str = "INFO" # Added log level setting
 
     # Piper Engine Timeouts (in seconds)
     PIPER_TIMEOUT_SECONDS: int = 30
     FFMPEG_TIMEOUT_SECONDS: int = 60
 
+    # Kokoro Engine Configuration
+    KOKORO_DEVICE: str = "cuda"  # or "cpu"
+    KOKORO_TIMEOUT_SECONDS: int = 30
+
+    # Coqui XTTS Engine Configuration
+    XTTS_DEVICE: str = "cuda"  # or "cpu"
+    XTTS_ACCEPT_LICENSE: bool = False  # User must opt-in
+    VOICES_DIR: str = "app/asset/voices" # Directory for reference speaker wavs
+
     model_config = SettingsConfigDict(env_file=".env", env_file_encoding='utf-8')
 
 settings = Settings()