feat(opencode): configure formatters and provide them on PATH

Add formatter entries for nix, prettier (md/yaml/json/web), shell,
python, toml and lua, and install the matching tools via the opencode
home module so they are available wherever opencode runs.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

modules/home/cli-apps/opencode/default.nix

@@ -1,6 +1,7 @@
 {
   lib,
   config,
+  pkgs,
   inputs,
   ...
 }:
@@ -29,6 +30,16 @@ in
   };
 
   config = mkIf cfg.enable {
+    # Formatters referenced by config/opencode/config.json; keep them on PATH for opencode.
+    home.packages = [
+      pkgs.nixfmt-rfc-style
+      pkgs.nodePackages.prettier
+      pkgs.shfmt
+      pkgs.ruff
+      pkgs.taplo
+      pkgs.stylua
+    ];
+
     xdg.configFile."opencode" = {
       source = ../../../../config/opencode;
       recursive = true;