docs(AGENTS): add required skills section for nix, nix-flakes, karpathy-guidelines

AGENTS.md

@@ -15,6 +15,13 @@ This is a **Nix flake overlay** repository that provides additional packages for
 3. Touch only what you must. Clean up only your own mess.
 4. Define success criteria. Loop until verified.
 
+### Required Skills
+
+Always use these skills when working with this repository:
+- **nix** - For nixpkgs package lookups, option searches, and NixOS/Home Manager queries
+- **nix-flakes** - For reproducible builds, flake management, and devShell operations
+- **karpathy-guidelines** - For high-quality task execution best practices
+
 ### Blueprint Framework
 
 This project uses `numtide/blueprint` which: