Add audiobookshelf-mcp package

Go binary from michaeldvinci/audiobookshelf-mcp (v0.0.5).
Covers libraries, audiobooks, podcasts, authors, collections,
playlists, and users. Uses buildGoModule with fakeHash placeholders
to be filled on first nix build.

packages/default.nix

@@ -20,5 +20,6 @@
   mcp-score = pkgs.callPackage ./mcp-score/package.nix { };
   applemusic-mcp = pkgs.callPackage ./applemusic-mcp/package.nix { };
   pinchflat-mcp = pkgs.callPackage ./pinchflat-mcp/package.nix { };
+  audiobookshelf-mcp = pkgs.callPackage ./audiobookshelf-mcp/package.nix { };
   # example-mcp-server = pkgs.callPackage ./example-mcp-server/package.nix { };
 }