Build: Web UI v1 — list / search / tag management (read-side)

[paperhurts]

Spec'd in spec.md §'Web UI' and tracked previously under #10.

Scope (v1 read-side)

• New package packages/web — Vite + React + Tailwind SPA, deployable to Cloudflare Pages or GitHub Pages.
• Same PAT model as the extensions (paste once, store in localStorage).
• Uses @gitmarks/core's GitHubClient with ETag conditional reads.
• Pages: list + client-side search + tag management.
• Aesthetic per spec: cyan/magenta on dark.

Out of scope (separate issue for v2)

• Bulk operations / trash view / Netscape HTML export — file as 'Web UI v2 write-side'.
• Bookmark creation in the web UI (spec explicitly excludes this; adding happens via extension on the actual page).

Acceptance

• Loads in a modern browser; reads bookmarks.json from the user's repo; renders the list.
• Search filters in-memory.
• Tag list editable via tags.json; renaming a tag updates tags.json without touching any bookmark (separate file by design).