fix(claude-plugin): clear "commands/ ignored" lint without breaking Antigravity

Claude Code v2.1.140+ flags the repo-root commands/ folder as "ignored" in
/doctor, `claude plugin list`, and the /plugin detail view, because
.claude-plugin/plugin.json points `commands` at ./.claude/commands (outside the
default folder) while a root commands/ still exists for Antigravity CLI.

List both locations explicitly so the default folder is no longer "ignored".
Per the plugins reference, the array form keeps the default and adds the custom
dir; the command loader only registers .md files, so Antigravity's
commands/*.toml are silently skipped (no extra Claude commands) and the lint
clears. No behavior change for Claude, Antigravity, or any other tool.

.claude-plugin/plugin.json

@@ -7,7 +7,7 @@
   "homepage": "https://github.com/addyosmani/agent-skills",
   "repository": "https://github.com/addyosmani/agent-skills",
   "license": "MIT",
-  "commands": "./.claude/commands",
+  "commands": ["./.claude/commands", "./commands"],
   "skills": "./skills",
   "agents": [
     "./agents/code-reviewer.md",