Cursor plugin specification and official plugins

Improve subagents per Cursor docs best practices master

- security-reviewer: add model/readonly, refine description with 'Use when', add When invoked section - ci-watcher: add model: fast, is_background: true, 'Use proactively' in description - browser-debugger: add model: fast, 'Use when' description, MCP browser tools mention Co-authored-by: Cursor <cursoragent@cursor.com>


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3 changed files