Unify agent config preparation with single get_agent() call
- Enhance get_agent() with include_datetime parameter for day vs interactive context
- Simplify prepare_config() to use single get_agent() call instead of redundant loading
- Remove separate _load_muse_meta() - frontmatter fields now directly in config
- Rename expand_tools to _expand_tools (private), update __all__
- Update hooks to use config directly instead of config["meta"]
- Update tests to check has_hook instead of has_meta
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>