fix(install): add Windows and CI compatibility

- Add get_venv_bin_dir() and activate_venv() helpers for cross-platform
  venv path handling (Scripts on Windows, bin on Unix)
- Replace all hardcoded venv activation calls with activate_venv
- Auto-install Python in non-interactive mode (CI) instead of prompting
  from /dev/tty which doesn't exist in CI environments
- Update configure_path grep to match both Windows and Unix venv paths
- Add setup-python to Linux CI jobs for faster, more reliable installs

Fixes Windows test failures with:
  install.sh: line 355: .../bin/activate: No such file or directory

Fixes Linux test failures with:
  install.sh: line 650: /dev/tty: No such device or address

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.github/workflows/install-script.yml

@@ -39,6 +39,11 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      - name: Setup Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.11'
+
       - name: Run install.sh ${{ matrix.mode }}
         run: bash install.sh ${{ matrix.mode }}