Register Explorer

Overview
The Register Explorer lets you browse and search Spectrum Next registers parsed from `data/nextreg.txt`. Each register page shows address, access details, bit tables, and notes.

Searching
- Use the search input to filter registers in real time.
- The query is case‑insensitive and matches a combined `search` field per register (name, address, and keywords).

Deep links (query string)
- The search box syncs with the `q` query parameter so searches are shareable.
- Example: `/registers?q=vram`
  - When you open this URL, the search box is pre‑filled with `vram` and the list is filtered immediately.
- Clearing the search removes `q` from the URL.

Implementation notes
- Component: `src/app/registers/RegisterBrowser.tsx`
- Uses Next.js navigation hooks: `useSearchParams`, `useRouter`, `usePathname`.
- On mount and when the URL changes, the component reads `q` and updates local state.
- On input change, the component updates state and calls `router.replace()` to keep the URL in sync without scrolling.
