The single-user notifications.md mechanism (a file in data/) died in the
multi-user move: assistant's prompt still pointed at it, but nothing read
it. Replace it with a memory note:
- event-triage injects user-memory/notifications.md verbatim on every
pass and treats it as authoritative over its default heuristics
- a shared common/notifications.md fragment, included by assistant, kid
and project-coordinator, tells the chat agents to record preference
requests there: one dated rule per bullet under a source heading or
General, asking for the source when ambiguous
- docs/system-agents.md explains the steering to users
