Add skillsmcp MCP server package

Update documentation in README.md and AGENTS.md
Refresh flake.lock for nixpkgs and flake-parts
Disable fastmcp checks to avoid version conflicts

packages/skillsmcp/default.nix

@@ -0,0 +1,4 @@
+{ pkgs, ... }:
+pkgs.callPackage ./package.nix {
+  fastmcp = pkgs.callPackage ./fastmcp.nix { };
+}