romm-mcp: restore library scans via POST /api/tasks/scan

romm_system action=scan threw client-side:

  Scan endpoint removed in RomM 5.0. Use the RomM web UI to trigger library scans.

That note is stale. The comment above the stub says RomM 5.0 removed POST
/api/tasks/run -- true -- but 5.4 serves POST /api/tasks/scan with a ScanPayload
(type, platforms, platform_fs_slugs, roms_ids, apis). Verified against the running
instance: /api/tasks/scan is in the 5.4.1 OpenAPI (226 paths), and a call with a
bad key answers 401 from that exact endpoint rather than 404.

So the stub was blocking a working endpoint, and scans still needed a human in the
UI. Patch restores runScan() defaulting to type=quick, which indexes new and
changed files without re-hashing the whole library (a full scan hashes 229 GB).

The patch targets dist/client.js: the npm tarball ships only dist/ plus a .d.ts, so
there is no .ts to patch without dragging in typescript. Keep it small and delete
it when upstream restores runScan().

packages/romm-mcp/package.nix

@@ -22,6 +22,12 @@ buildNpmPackage rec {
 
   postPatch = ''
     cp ${./package-lock.json} package-lock.json
+
+    # romm_system action=scan was stubbed out client-side ("Scan endpoint removed in
+    # RomM 5.0"), but RomM 5.4 restored POST /api/tasks/scan, so the stub only blocks a
+    # working endpoint. Upstream publishes no sources in the npm tarball, so this patches
+    # the compiled dist/ directly; drop it once upstream restores runScan().
+    patch -p1 < ${./romm-mcp-scan.patch}
   '';
 
   # dist/*.js (tsc output) ships inside the npm tarball, so there is nothing to