feat: add opencode, comment-checker packages; update README and flake.lock

- Add opencode and comment-checker to home packages
- Package comment-checker via prebuilt GitHub Releases binaries
- Register comment-checker overlay and flake packages output
- Add flake.lock to pin dependency versions
- Update README to match actual repo structure
- Add Node.js version notes in languages.nix

home/default.nix

@@ -47,6 +47,10 @@
     nvd # nix version diff
     nh # nix helper (nixos-rebuild wrapper)
 
+    # AI coding agent
+    opencode
+    comment-checker # AI code comment detection hook
+
     # Misc
     micro # simple editor fallback
   ];

home/dev/languages.nix

@@ -3,6 +3,8 @@
 {
   home.packages = with pkgs; [
     # ── Language runtimes ──
+    # Node.js: 默认跟随 nixpkgs，当前 unstable 为 v24.14.0
+    # 如需固定 LTS 版本，改为: nodejs_22 或 nodejs_20
     nodejs
     go
     bun