Enable CUDA for Windows/Linux builds + clean up old sidecars

- Windows and Linux sidecar builds now use --with-cuda for GPU acceleration
  (macOS stays CPU-only — Apple Silicon uses Metal, not CUDA)
- Windows upload switched from --data-binary to -T streaming for 2GB+ files
- Add cleanup_old_sidecars() that removes stale sidecar-* directories on
  startup, keeping only the current version
- Add NSIS uninstall hook to remove sidecar data dir on Windows uninstall
  (user data in ~/.voicetonotes is preserved)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitea/workflows/release.yml

@@ -114,7 +114,7 @@ jobs:
 
       - name: Build sidecar
         working-directory: python
-        run: uv run --python ${{ env.PYTHON_VERSION }} python build_sidecar.py --cpu-only
+        run: uv run --python ${{ env.PYTHON_VERSION }} python build_sidecar.py --with-cuda
 
       - name: Package sidecar for Tauri
         run: |
@@ -217,7 +217,7 @@ jobs:
       - name: Build sidecar
         shell: powershell
         working-directory: python
-        run: uv run --python ${{ env.PYTHON_VERSION }} python build_sidecar.py --cpu-only
+        run: uv run --python ${{ env.PYTHON_VERSION }} python build_sidecar.py --with-cuda
 
       - name: Package sidecar for Tauri
         shell: powershell
@@ -286,7 +286,7 @@ jobs:
               -X POST `
               -H "Authorization: token $env:BUILD_TOKEN" `
               -H "Content-Type: application/octet-stream" `
-              --data-binary "@$($_.FullName)" `
+              -T "$($_.FullName)" `
               "$uploadUrl" 2>&1
             if ($LASTEXITCODE -eq 0) {
               Write-Host "Upload successful: ${filename}"