New AgentConfig dataclass in config.py with fields:
- name, display_name, personality_file, model
- tools (whitelist), skills (filter), memory_scope
Loaded from config.yaml under agents: key. Defaults to single
agent for backward compatibility when section is omitted.
config.yaml now includes 4 agent configs: default, writer,
researcher, ops — each with appropriate tool/skill whitelists.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>