Install Playwright browsers in CI for web tests

The web extension tests use @vscode/test-web which requires Playwright
to run browser-based tests. Add explicit Playwright chromium installation
step before running web tests.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: ntotten

.github/workflows/main.yaml

@@ -51,6 +51,7 @@ jobs:
           node-version-file: ".nvmrc"
       - uses: pnpm/action-setup@v4
       - run: pnpm install
+      - run: pnpm exec playwright install chromium
       - run: pnpm test:web
   package:
     runs-on: ubuntu-latest