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)

.github/workflows/ci.yml

@@ -0,0 +1,20 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: cachix/install-nix-action@v27
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
+      - name: Flake check (formatting + evaluation)
+        run: nix flake check
+      - name: Build all packages (best-effort, may time out)
+        run: nix build .#packages || true