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.nix

@@ -6,7 +6,7 @@
   };
 
   inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
     systems.url = "github:nix-systems/default";
     blueprint = {
       url = "github:numtide/blueprint";
@@ -40,9 +40,21 @@
         nixpkgs.config.allowUnfree = true;
       };
 
+      extraPackages = inputs.nixpkgs.lib.genAttrs (builtins.attrNames blueprintOutputs.packages) (
+        system:
+        let
+          pkgs = inputs.nixpkgs.legacyPackages.${system};
+        in
+        {
+          container-use = pkgs.callPackage ./packages/container-use/package.nix { };
+        }
+      );
+
     in
     blueprintOutputs
     // {
+      packages = inputs.nixpkgs.lib.recursiveUpdate blueprintOutputs.packages extraPackages;
+
       overlays = {
         default = import ./overlays {
           inherit (blueprintOutputs) packages;