fix: improve package quality and fix goose-cli build

- Add meta.platforms to all packages for proper platform detection
- Add passthru.category to mcp-gateway for consistency
- Fix meta style inconsistency in mcp-gateway (lib.licenses → licenses)
- Fix pythonImportsCheck in skillsmcp to actually validate the import
- Remove empty maintainers list from skillsmcp
- Add libclang to goose-cli nativeBuildInputs (fixes bindgen/llama-cpp-sys-2 build)
- Add treefmt.toml with nixfmt formatter configuration
- Add nixConfig.extra-substituters for binary cache support
- Delete broken goose-cli/update.py (referenced missing scripts/updater.py)
- Document nix-update usage in AGENTS.md for package updates
- Fix stale project structure diagram in README

packages/goose-cli/package.nix

@@ -8,6 +8,7 @@
   dbus,
   versionCheckHook,
   librusty_v8,
+  llvmPackages,
 }:
 
 rustPlatform.buildRustPackage rec {
@@ -23,7 +24,10 @@ rustPlatform.buildRustPackage rec {
 
   cargoHash = "sha256-fN0FKDYFkZrQQPWdUlemOaGzIAZhqFyskz9TEmG+X4o=";
 
-  nativeBuildInputs = [ pkg-config ];
+  nativeBuildInputs = [
+    pkg-config
+    llvmPackages.libclang
+  ];
 
   buildInputs = [
     openssl
@@ -35,6 +39,9 @@ rustPlatform.buildRustPackage rec {
   # To avoid this we pre-download the file and export it via RUSTY_V8_ARCHIVE
   env.RUSTY_V8_ARCHIVE = librusty_v8;
 
+  # bindgen (used by llama-cpp-sys-2) needs libclang
+  env.LIBCLANG_PATH = llvmPackages.libclang.lib;
+
   # Build only the CLI package
   cargoBuildFlags = [
     "--package"
@@ -67,5 +74,6 @@ rustPlatform.buildRustPackage rec {
     license = licenses.asl20;
     sourceProvenance = with sourceTypes; [ fromSource ];
     mainProgram = "goose";
+    platforms = platforms.all;
   };
 }