Add pinchflat-mcp package

Python MCP server (fastmcp + httpx) that exposes the Pinchflat REST API
as MCP tools. Covers sources, media items, media profiles, tasks, and
settings endpoints.

Tested against live Pinchflat instance — 28 sources, search, app info
all working via stdio transport.

packages/default.nix

@@ -19,5 +19,6 @@
   annas-mcp = pkgs.callPackage ./annas-mcp/package.nix { };
   mcp-score = pkgs.callPackage ./mcp-score/package.nix { };
   applemusic-mcp = pkgs.callPackage ./applemusic-mcp/package.nix { };
+  pinchflat-mcp = pkgs.callPackage ./pinchflat-mcp/package.nix { };
   # example-mcp-server = pkgs.callPackage ./example-mcp-server/package.nix { };
 }