feat: init:agent command to set up MCP and skills for coding agents

[DavertMik]

Summary

Adds npx codeceptjs init:agent [agent] (alias init-agent). It registers the CodeceptJS MCP server and installs the CodeceptJS skills for a coding agent, using the agent's own commands where it has them.

Base branch is 4.x: the MCP server and agent docs exist only there.

npx codeceptjs init:agent              # pick from a list
npx codeceptjs init:agent claude       # claude | codex | cursor | opencode
npx codeceptjs init --agent claude     # full init, then agent setup

What each agent gets

Agent	MCP	Skills
claude	claude mcp add codeceptjs -- npx codeceptjs-mcp	npx skills add codeceptjs/skills -a claude-code -y
codex	codex mcp add codeceptjs -- npx codeceptjs-mcp	npx skills add codeceptjs/skills -a codex -y
cursor	adds mcpServers.codeceptjs to .cursor/mcp.json	npx skills add codeceptjs/skills -a cursor -y
opencode	adds mcp.codeceptjs to opencode.json	npx skills add codeceptjs/skills -a opencode -y

• Commands run with execSync. If one fails, the error and the command to run by hand are printed, and setup continues.
• Cursor/OpenCode files keep their other keys. A file that isn't valid JSON is left untouched and the entry to add is printed.
• init gets --agent <name> and ends with "Set up an AI coding agent?" (default none). With -y and no --agent it's skipped.
• Docs: docs/agents.md leads with init:agent, manual steps moved under "Manual setup"; docs/mcp.md and docs/commands.md mention it.

Test plan

• test/unit/command/initAgent_test.js: fake claude/codex/npx binaries on PATH record their arguments. Covers claude and codex commands, skills still installed when MCP fails, cursor/opencode merge, same file on second run, invalid JSON untouched, unknown agent and -y without agent.
• npx mocha test/unit/command: 34 passing
• eslint and prettier clean on the new files

🤖 Generated with Claude Code