Run full bootstrap in integration tests; fix pnpm setup shell detection

- Integration tests now run the full bootstrap (system + flatpak + custom +
  AI + VM packages) instead of '--only custom --no-vm --no-ai', so that
  custom-package prerequisites (zsh, gh, etc.) installed via SystemPackages
  are actually available.
- Fix 'pnpm setup' failing with ERR_PNPM_UNKNOWN_SHELL in CI containers
  by exporting SHELL=/bin/bash before invoking it.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/workflows/integration.yml

@@ -59,7 +59,7 @@ jobs:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
-          echo y | ./bootstrap_environment --only custom --no-vm --no-ai
+          echo y | ./bootstrap_environment
 
   conclusion:
     name: Final Status Check