Remove pre-streams path fallbacks
Remove the dead two-level agents markdown formatter pattern that no longer matches migrated journals.
Rename segment_dir to agents_dir in muse/entities.py to match what the variable actually holds.
Update the activity_state output-path docstring to include the stream level, require stream in load_previous_state, _list_facets_with_activity_state, and _load_activity_state, and remove the old day_path fallback branches and unused import.