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>

Readme.md

@@ -65,12 +65,29 @@ https://platform.openai.com/docs/quickstart/account-setup
 
 6. You can change the API key at any time under the 'Settings' menu.
 
+7. (Optional) You can also configure a custom API Base URL under 'Settings > API Base URL' to use compatible API endpoints other than OpenAI. For example, to use SiliconFlow's API, set the base URL to `https://api.siliconflow.cn/v1` (Note: use just the base URL, NOT the full endpoint path). Leave empty to use OpenAI's default endpoint.
+
+8. (Optional) You can select different TTS models from the "TTS Model" dropdown. When using SiliconFlow, the CosyVoice2-0.5B model will be available with 8 built-in voices (alex, anna, bella, benjamin, charles, claire, david, diana). The voice options will update automatically based on the selected model.
+
+9. (Optional) The Voice dropdown supports both selecting from the list and typing custom voice IDs. Click on the voice field to type a custom voice ID (e.g., for SiliconFlow custom voices like `speech:your-voice-name:xxxx`). This is useful if you've uploaded custom voice samples to SiliconFlow.
+
 This tool was brought to you by Scorchsoft - We build custom apps to your requirements. Please contact us if you have a requirement for a custom app project.
 
 ## Advanced Tips
 
 
-### 1. ChatGPT AI Manipulation
+### 1. Custom Voices with SiliconFlow
+
+When using SiliconFlow's API, you can upload your own voice samples and use them by entering the custom voice ID in the Voice dropdown. To upload a custom voice:
+
+1. Upload your voice sample to SiliconFlow (see their documentation)
+2. You'll receive a voice ID like: `speech:your-voice-name:cm04pf7az00061413w7kz5qxs:mjtkgbyuunvtybnsvbxd`
+3. Click on the Voice dropdown and type/paste this custom voice ID
+4. The app will use this custom voice for TTS
+
+For more information on uploading custom voices, see: [SiliconFlow Text-to-Speech Documentation](https://docs.siliconflow.cn/en/userguide/capabilities/text-to-speech)
+
+### 2. ChatGPT AI Manipulation
 
 If you go to "Settings > ChatGPT Manipulation" then you can turn this on and pick which model to use.
 
@@ -104,6 +121,22 @@ run the executable or "python text-to-mic.py"
 https://vb-audio.com/Cable/
 
 ## 2) ensure the OpenAI API key is specified in the .env file
+You can also optionally set `OPENAI_API_BASE_URL` in the .env file to use a compatible API endpoint other than OpenAI. For example, to use SiliconFlow's API:
+```
+OPENAI_API_KEY=your_api_key_here
+OPENAI_API_BASE_URL=https://api.siliconflow.cn/v1
+OPENAI_TTS_MODEL=FunAudioLLM/CosyVoice2-0.5B
+```
+**Important:** Use just the base URL (e.g., `https://api.siliconflow.cn/v1`), NOT the full endpoint path (don't add `/audio/speech`).
+
+Leave `OPENAI_API_BASE_URL` empty to use OpenAI's default endpoint.
+
+Available TTS models:
+- `tts-1` (OpenAI standard, default)
+- `tts-1-hd` (OpenAI high quality)
+- `gpt-4o-mini-tts` (OpenAI)
+- `FunAudioLLM/CosyVoice2-0.5B` (SiliconFlow - multi-language, emotional TTS)
+
 This sets up a virtual microphone that we can use to sent text to speech audio to. Then, when you join a meeting, such as a google meeting, you can select this virtual cable to hear the audio being sent on the channel.
 
 ## 3) Run the script: