Add facet merge journal command
Add `sol call journal facet merge SOURCE --into DEST [--consent]` to merge entities, open todos, calendar events, and news into a destination facet before deleting the source facet. Reuse canonical observation helpers for atomic writes, and cover the entity-conflict merge branch plus the rest of the merge flow in tests. Document the facet merge command and the related entity, calendar, and todo move commands in SKILL.md and unified.md.