Fix macOS CI and remove duplicate GitHub Actions workflow

- Set AGENT_TOOLSDIRECTORY via step-level env on setup-python (not
  GITHUB_ENV which only applies to subsequent steps)
- Use runner.temp for toolcache dir (always writable, no sudo needed)
- Remove .github/workflows/build.yml to prevent duplicate CI runs
- Remove unused Windows env check step

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

.gitea/workflows/build.yml

@@ -32,16 +32,12 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - name: Set up Python toolcache (macOS)
-        if: matrix.platform == 'macos'
-        run: |
-          mkdir -p ${{ github.workspace }}/.toolcache
-          echo "AGENT_TOOLSDIRECTORY=${{ github.workspace }}/.toolcache" >> $GITHUB_ENV
-
       - name: Set up Python
         uses: actions/setup-python@v5
         with:
           python-version: ${{ env.PYTHON_VERSION }}
+        env:
+          AGENT_TOOLSDIRECTORY: ${{ runner.temp }}/toolcache
 
       - name: Install Python build tools
         run: python -m pip install --upgrade pip setuptools wheel
@@ -97,13 +93,6 @@ jobs:
         run: |
           brew install --quiet create-dmg || true
 
-      - name: Install system dependencies (Windows)
-        if: matrix.platform == 'windows'
-        shell: powershell
-        run: |
-          # Ensure Visual Studio Build Tools are available (usually pre-installed on runners)
-          Write-Host "Windows build environment ready"
-
       - name: Download sidecar artifact
         uses: actions/download-artifact@v3
         with: