feat: add CosyVoice2/3 TTS engine with instruct and voice cloning

Integrate Alibaba's CosyVoice2-0.5B and Fun-CosyVoice3-0.5B as a new
TTS engine supporting 9 languages, zero-shot voice cloning, and instruct
control (emotions, speed, volume, dialects).

The CosyVoice source is cloned at setup time into backend/vendors/ since
no PyPI package exists. A modelscope→HuggingFace shim redirects model
downloads to the public HF repos, and a lightweight pylogger shim avoids
pulling in pytorch-lightning as a transitive dependency.

Backend: cosyvoice_backend.py, __init__.py registry, models.py regex
Frontend: engine selector, language map, Zod schema, model descriptions
Infra: requirements.txt, justfile, release.yml, Dockerfile, PyInstaller

.github/workflows/release.yml

@@ -63,6 +63,7 @@ jobs:
           pip install -r backend/requirements.txt
           pip install --no-deps chatterbox-tts
           pip install --no-deps hume-tada
+          git clone --recursive --depth 1 https://github.com/FunAudioLLM/CosyVoice.git backend/vendors/CosyVoice
 
       - name: Install MLX dependencies (Apple Silicon only)
         if: matrix.backend == 'mlx'
@@ -190,6 +191,7 @@ jobs:
           pip install -r backend/requirements.txt
           pip install --no-deps chatterbox-tts
           pip install --no-deps hume-tada
+          git clone --recursive --depth 1 https://github.com/FunAudioLLM/CosyVoice.git backend/vendors/CosyVoice
 
       - name: Install PyTorch with CUDA 12.6
         run: |