feat(packages): add relay-free-llm package

Add RelayFreeLLM, a RESTful API gateway that routes prompts to multiple
AI providers (Gemini, Cerebras, Groq, Mistral, etc.) with failover and
intent-based routing. Includes local cerebras-cloud-sdk build since it is
not yet in nixpkgs.

packages/relay-free-llm/default.nix

@@ -0,0 +1,5 @@
+{
+  pkgs,
+  ...
+}:
+pkgs.callPackage ./package.nix { }