Initial commit: MCP server packages for Nix

- Add flake structure with overlay and packages exports
- Add manim-mcp-server as first packaged MCP server
- Add README.org with usage instructions and package templates
- Add packages/default.nix as package aggregator
- Add overlays/default.nix for nixpkgs integration

packages/default.nix

@@ -0,0 +1,16 @@
+# MCP Server Packages
+#
+# This file aggregates all MCP server packages in this repository.
+# To add a new package:
+#   1. Create a directory: packages/<package-name>/
+#   2. Create package.nix in that directory
+#   3. Add an entry below using callPackage
+#
+{ pkgs }:
+
+{
+  manim-mcp-server = pkgs.callPackage ./manim-mcp-server/package.nix { };
+
+  # Add new packages here:
+  # example-mcp-server = pkgs.callPackage ./example-mcp-server/package.nix { };
+}