fix: resolve code quality issues, add CI, and improve maintainability

- Remove useless nixConfig block (cache.nixos.org is default)
- Remove manual container-use override; let blueprint auto-discover it
- Add nixosModules.default so README example works
- Fix default launcher: use correct parameterized flake URL
- Replace deprecated sha256 with hash in goose-cli fetchers
- Fix LIBCLANG_PATH to include /lib subdirectory for libclang.so
- Drop --release from goose-cli tests (faster, more debug info)
- Use builtins.toFile in flake-inputs to avoid ARG_MAX risk
- Add lib.warn when overlay has no packages for a system
- Add passthru.updateScript to goose-cli, container-use, skillsmcp
- Fix skillsmcp version to 0.2.0+unstable (pinned to commit, not tag)
- Replace with lib; with explicit references in all meta blocks
- Add update.py script for goose-cli (referenced in AGENTS.md)
- Expand .gitignore with result-* and .direnv/
- Add GitHub Actions CI workflow (nix flake check + build)

flake.nix

@@ -1,10 +1,6 @@
 {
   description = "Various packages for Nix";
 
-  nixConfig = {
-    extra-substituters = [ "https://cache.nixos.org" ];
-  };
-
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
     systems.url = "github:nix-systems/default";
@@ -33,28 +29,17 @@
   };
 
   outputs =
-    inputs:
+    { self, ... }@inputs:
     let
       blueprintOutputs = inputs.blueprint {
         inherit inputs;
+        # allowUnfree is needed for packages that depend on pre-built
+        # binaries (e.g., goose-cli's librusty_v8)
         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;
@@ -63,5 +48,9 @@
           inherit (blueprintOutputs) mkPackagesFor;
         };
       };
+
+      nixosModules.default = {
+        nixpkgs.overlays = [ self.overlays.default ];
+      };
     };
 }