ci(build): 🎡 activate virtualenv before running build script

Ensure the build job activates the repository virtual environment before invoking src/proxy_app/build.py. This guarantees the correct Python interpreter and installed dependencies (e.g., PyInstaller) are available across runner environments by attempting .venv/bin/activate then .venv/Scripts/activate.

.github/workflows/build.yml

@@ -71,7 +71,10 @@ jobs:
           ${{ runner.os }}-pyinstaller-3.12-
 
     - name: Build executable
-      run: python src/proxy_app/build.py
+      shell: bash
+      run: |
+        source .venv/bin/activate || . .venv/Scripts/activate
+        python src/proxy_app/build.py
 
     - name: Ensure PyInstaller cache directory exists
       shell: pwsh