feat: add event notes with pending state, 5-min TTL, cancel, and /note command

internal/db/store.go

@@ -570,6 +570,12 @@ func (s *Store) EventsForDayByDate(userID int64, date string) ([]Event, error) {
 	return events, rows.Err()
 }
 
+// SetEventNote updates the note for an event.
+func (s *Store) SetEventNote(eventID int64, note string) error {
+	_, err := s.db.Exec("UPDATE events SET note=? WHERE id=?", note, eventID)
+	return err
+}
+
 // EventsForDayByDayID returns all events for a day record, ordered by occurrence.
 func (s *Store) EventsForDayByDayID(dayID int64) ([]Event, error) {
 	rows, err := s.db.Query(`