Replaces the four-value enum (community/workshop/social/showcase) with
seven values: talk, workshop, community-meetup, coworking, peer-session,
skills-share, info-session. Default is now community-meetup.
Adds app/config/eventTypes.js as the single source of truth for value→label
mapping. Updates the model enum, seed scripts, and admin event list/filter
+ admin dashboard to read from it via EVENT_TYPES and eventTypeLabel().