Fix remaining CI issues

- Use unique artifact names in binaries.yml to avoid upload conflicts.
- Standardize pip installation in ci/test-e2e.sh.
- Fix hardcoded paths in ci/test-e2e.sh and ensure it uses correct demosite folder.
- Ensure E2E tests in tests/test_e2e.py correctly patch _locale_res and use absolute paths for source assets.

.github/workflows/binaries.yml

@@ -97,7 +97,7 @@ jobs:
       - name: Upload artifacts
         uses: actions/upload-artifact@v4
         with:
-          name: ${{ matrix.asset_name }}
+          name: binaries-${{ matrix.os }}
           path: |
             dist/${{ matrix.artifact_name }}
             voxvera/resources/bin/*.deb