Update release workflow and model references

- Added a step to install PyTorch with CUDA for Windows in the release workflow.
- Updated model references in backend/main.py to use openai/whisper models instead of mlx-community for the MLX backend.

.github/workflows/release.yml

@@ -66,6 +66,12 @@ jobs:
         run: |
           pip install -r backend/requirements-mlx.txt
 
+      - name: Install PyTorch with CUDA (Windows only)
+        if: matrix.platform == 'windows-latest'
+        run: |
+          pip install torch --index-url https://download.pytorch.org/whl/cu121 --force-reinstall --no-deps
+          pip install torchvision torchaudio --index-url https://download.pytorch.org/whl/cu121
+
       - name: Build Python server (Linux/macOS)
         if: matrix.platform != 'windows-latest'
         run: |