coral-extend

Add a new component to the CORAL framework itself — a new agent runtime under coral/agent/builtin/ (claude_code/codex/cursor_agent style), a new CLI command in coral/cli/, a new bundled skill or subagent template under coral/template/skills/ or coral/template/agents/, a new hook in coral/hooks/, a new field in coral/config.py, or a framework-level extension to the grader stack under coral/grader/. NOT for writing a…