Add romm-mcp package

RomM MCP server: browse, search and administrate a self-hosted ROM library,
including triggering library scans (POST /api/tasks/scan), which RomM 5.x only
exposes through its API.

Upstream ships no package-lock.json, so the lock committed here is generated from
the published 1.0.5 tarball (npm install --package-lock-only --ignore-scripts),
pinning exactly the tree that shipped with that version. dist/ is prebuilt in the
tarball, hence dontNpmBuild.

npmDepsHash is a placeholder: it can only be derived from the lockfile by a build,
so CI (nix flake check, which builds every package) reports the real value.

packages/default.nix

@@ -33,5 +33,6 @@
   pdf-mcp = pkgs.callPackage ./pdf-mcp/package.nix { };
   mcp-searxng = pkgs.callPackage ./mcp-searxng/package.nix { };
   python-ssh-mcp = pkgs.callPackage ./python-ssh-mcp/package.nix { };
+  romm-mcp = pkgs.callPackage ./romm-mcp/package.nix { };
   # example-mcp-server = pkgs.callPackage ./example-mcp-server/package.nix { };
 }