Use uv for Python management in CI and build script

- CI: install uv via astral-sh/setup-uv, use uv to install Python
  and run the build script (replaces setup-python which fails on
  self-hosted macOS runners)
- build_sidecar.py: auto-detects uv and uses it for venv creation
  and package installation (much faster), falls back to standard
  venv + pip when uv is not available
- Remove .github/workflows duplicate

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/build.yml

@@ -32,19 +32,15 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - name: Set up Python
-        uses: actions/setup-python@v5
-        with:
-          python-version: ${{ env.PYTHON_VERSION }}
-        env:
-          AGENT_TOOLSDIRECTORY: ${{ runner.temp }}/toolcache
+      - name: Install uv
+        uses: astral-sh/setup-uv@v4
 
-      - name: Install Python build tools
-        run: python -m pip install --upgrade pip setuptools wheel
+      - name: Set up Python
+        run: uv python install ${{ env.PYTHON_VERSION }}
 
       - name: Build sidecar
         working-directory: python
-        run: python build_sidecar.py --cpu-only
+        run: uv run --python ${{ env.PYTHON_VERSION }} python build_sidecar.py --cpu-only
 
       - name: Upload sidecar artifact
         uses: actions/upload-artifact@v3