Improve ZXDB downloads with local mirroring and inline preview

This commit implements a comprehensive local file mirror system for
ZXDB and WoS downloads, allowing users to access local archives
directly through the explorer UI.

Key Changes:

Local File Mirroring & Proxy:
- Added `ZXDB_LOCAL_FILEPATH` and `WOS_LOCAL_FILEPATH` to `src/env.ts`
  and `example.env` for opt-in local mirroring.
- Implemented `resolveLocalLink` in `src/server/repo/zxdb.ts` to map
  database `file_link` paths to local filesystem paths based on
  configurable prefixes.
- Created `src/app/api/zxdb/download/route.ts` to safely proxy local
  files, preventing path traversal and serving with appropriate
  `Content-Type` and `Content-Disposition`.
- Updated `docs/ZXDB.md` with setup instructions and resolution logic.

UI Enhancements & Grouping:
- Grouped downloads and scraps by type (e.g., Inlay, Game manual, Tape
  image) in `EntryDetail.tsx` and `ReleaseDetail.tsx` for better
  organization.
- Introduced `FileViewer.tsx` component to provide inline previews
  for supported formats (.txt, .nfo, .png, .jpg, .gif, .pdf).
- Added a "Preview" button for local mirrors of supported file types.
- Optimized download tables with badge-style links for local/remote
  sources.

Guideline Updates:
- Updated `AGENTS.md` to clarify commit message handling: edit or
  append to `COMMIT_EDITMSG` instead of overwriting.
- Re-emphasized testing rules: use `tsc --noEmit`, do not restart
  dev-server, and avoid `pnpm build` during development.

Signed-off-by: junie@lucy.xalior.com

example.env

@@ -19,9 +19,6 @@ ZXDB_REMOTE_FILEPATH=https://zxdbfiles.com/
 # Note: Example uses the Internet Archive WoS mirror; keep the trailing slash
 WOS_REMOTE_FILEPATH=https://archive.org/download/World_of_Spectrum_June_2017_Mirror/World%20of%20Spectrum%20June%202017%20Mirror.zip/World%20of%20Spectrum%20June%202017%20Mirror/
 
-# Local cache root where files will be mirrored (without the leading slash)
-CDN_CACHE=/mnt/files/zxfiles
-
 # Local mirror filesystem paths for downloads.
 # Enabling these (and verifying existence) will show "Local Mirror" links.
 # See docs/ZXDB.md for how prefixes are stripped and joined to these paths.