feat: add container-use package and fix goose-cli libclang dependency

- Add dagger/container-use (v0.4.2) for containerized coding agent environments
- Fix goose-cli build by adding llvmPackages.libclang for bindgen
- Clean up skillsmcp package (remove custom fastmcp override, use nixos-unstable)
- Remove broken update.py script from goose-cli
- Add treefmt.toml for consistent formatting
- Update README with all current packages

flake.lock

@@ -75,16 +75,16 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1777946660,
-        "narHash": "sha256-iw3XDIG6xxk+AZTcawCLHf6i9i4tXRzLZEoV9xhRToQ=",
+        "lastModified": 1777954456,
+        "narHash": "sha256-hGdgeU2Nk87RAuZyYjyDjFL6LK7dAZN5RE9+hrDTkDU=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "bc57abace07689cfd34203aa5fb4027514895987",
+        "rev": "549bd84d6279f9852cae6225e372cc67fb91a4c1",
         "type": "github"
       },
       "original": {
         "owner": "NixOS",
-        "ref": "nixpkgs-unstable",
+        "ref": "nixos-unstable",
         "repo": "nixpkgs",
         "type": "github"
       }