feat: Add SiliconFlow TTS API support with custom base URL and model selection

This commit adds comprehensive support for using SiliconFlow's TTS API as an alternative to OpenAI, including:

Features:
- Configurable API base URL (Settings > API Base URL)
- TTS model selection dropdown (CosyVoice2-0.5B, OpenAI compatible models)
- Dynamic voice options based on selected model
- Editable voice dropdown (Combobox) supporting custom voice IDs
- Automatic voice formatting for SiliconFlow (model:voice format)
- Debug logging for troubleshooting API calls
- Warning for incorrect base URL format

Changes:
- utils/settings_manager.py: Added api_base_url and tts_model settings
- utils/text_to_mic.py:
  - Added get_available_tts_models() for model options
  - Added get_siliconflow_voices() for SiliconFlow voices
  - Added change_api_base_url() method with validation
  - Added TTS model dropdown in GUI
  - Converted voice dropdown to Combobox for typing support
  - Added on_voice_exit() for validation
  - Updated API call to use selected model and formatted voice
- text-to-mic-cli.py: Added OPENAI_API_BASE_URL and OPENAI_TTS_MODEL env var support
- Readme.md: Updated documentation with SiliconFlow usage instructions

Supported Models:
- FunAudioLLM/CosyVoice2-0.5B (SiliconFlow - multi-language, emotional)
- tts-1, tts-1-hd (OpenAI compatible)
- gpt-4o-mini-tts (OpenAI default)

SiliconFlow Voices (CosyVoice2-0.5B):
- Male: alex, benjamin, charles, david
- Female: anna, bella, claire, diana
- Custom voices via voice ID entry

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

text-to-mic-cli.py

@@ -10,7 +10,14 @@ import os
 load_dotenv()
 
 # Set up your OpenAI API key from the environment variable
-client = OpenAI(api_key=os.getenv('OPENAI_API_KEY'))
+api_key = os.getenv('OPENAI_API_KEY')
+api_base_url = os.getenv('OPENAI_API_BASE_URL', '').strip()
+
+# Create client with custom base URL if provided
+if api_base_url:
+    client = OpenAI(api_key=api_key, base_url=api_base_url)
+else:
+    client = OpenAI(api_key=api_key)
 
 def list_audio_devices():
     p = pyaudio.PyAudio()
@@ -81,9 +88,13 @@ def play_audio_multiplexed(file_paths, device_indices):
     
     p.terminate()
     
-def stream_audio_to_virtual_mic(text, voice="fable", device_index=None, device_index_2=None):
+def stream_audio_to_virtual_mic(text, voice="fable", model=None, device_index=None, device_index_2=None):
+    # Get model from environment variable or use default
+    if model is None:
+        model = os.getenv('OPENAI_TTS_MODEL', 'tts-1')
+
     response = client.audio.speech.create(
-        model="tts-1",
+        model=model,
         voice=voice,
         input=text,
         response_format='wav'
@@ -114,10 +125,27 @@ if __name__ == "__main__":
 
     if arglen < 2:
         print("Usage: python script.py 'text to convert'")
+        print("Environment variables:")
+        print("  OPENAI_API_KEY - Your API key (required)")
+        print("  OPENAI_API_BASE_URL - Custom API base URL (optional)")
+        print("  OPENAI_TTS_MODEL - TTS model to use (default: tts-1)")
+        print("")
+        print("Example models:")
+        print("  - tts-1 (OpenAI standard)")
+        print("  - tts-1-hd (OpenAI high quality)")
+        print("  - gpt-4o-mini-tts (OpenAI)")
+        print("  - FunAudioLLM/CosyVoice2-0.5B (SiliconFlow)")
+        print("")
+        print("For SiliconFlow voices with CosyVoice2:")
+        print("  The voice will be auto-formatted as: FunAudioLLM/CosyVoice2-0.5B:alex")
         sys.exit(1)
-    
+
     print(f"arg count {arglen}")
 
+    # Get TTS model from environment
+    tts_model = os.getenv('OPENAI_TTS_MODEL', 'tts-1')
+    print(f"Using TTS model: {tts_model}")
+
     if arglen == 4:
         device_index = int(sys.argv[2])
         device_index_2 = int(sys.argv[3])
@@ -129,5 +157,5 @@ if __name__ == "__main__":
         device_index = int(input("Enter the device index: "))
         device_index_2 = None
 
-    
-    stream_audio_to_virtual_mic(sys.argv[1], voice="fable", device_index=device_index,device_index_2=device_index_2)
+
+    stream_audio_to_virtual_mic(sys.argv[1], voice="fable", model=tts_model, device_index=device_index,device_index_2=device_index_2)