When the browser binary is missing (fresh install, first run), detect
the error and run `playwright install <channel>` automatically instead
of erroring out. On Linux with root, also attempts `install-deps`.
- New src/browserInstaller.ts module with install deduping and caching
- Wired into isolated and persistent context launch paths
- Wired into video-recording launch path in context.ts
- Clear error if playwright npm package itself isn't resolvable
