feat: persist git-fsa directory handle

[lux-in-tenebris-lucet]

Summary

Update the browser Git + File System Access demo so it can remember and reopen the selected folder.

This pattern is useful for browser-based Git clients, editors, IDEs, local-first apps, and content tools that work directly with user folders. Those products can resume the same folder after a reload instead of asking users to select it again or accidentally initializing the demo repository twice.

What changed

• Store the selected directory handle in IndexedDB.
• Restore access automatically when permission remains granted.
• Provide reconnect and forget actions when permission must be restored.
• Reopen an existing demo repository without creating another initial commit.
• Repair the demo's browser build after the monorepo migration and remove its unused worker.
• Document the run command and manual test flow.

Why

The existing demo was a one-time flow: it forgot the selected folder on reload and always tried to create a new /repo directory. Its browser build also referenced an old worker path and did not handle the node: imports used by the current workspace packages.

Testing

• yarn test — 87 suites and 1,244 tests passed
• yarn typecheck
• yarn prettier:check
• yarn build
• yarn workspace memfs webpack --config ./demo/git-fsa/webpack.config.js
• Manually created the demo repository, reloaded the page, reopened the saved folder, and verified that only one initial commit existed

[streamich]

Thank you!