Add first-class Codex setup support

[byapparov]

Summary

• Add Codex as a supported editor in CLI parsing and the interactive selector.
• Install a Codex local plugin with fetched aictrl skills and register it in the personal marketplace.
• Merge an aictrl Codex MCP config using bearer_token_env_var = "AICTRL_API_KEY" and document the current Codex telemetry limitation.

Closes #24

Test plan

• npm test
• npm run build
• Generated Codex plugin validated with the Codex plugin validator