feat(admin): events & sessions

Summary

Event lifecycle management — creation, approval, committee assignment, session scheduling, attendance tracking, sponsor wiring. Largest subsystem. Likely needs decomposition into sub-issues during its own brainstorm.

Requirements

• Brainstorming → spec under docs/superpowers/specs/. (Likely splits into 2–3 sub-specs.)
• /admin/events — global list (staff+); event chairs see only events they chair.
• Event creation flow: draft → submitted → approved → published, with status enum and approval gate.
• /admin/events/:id — detail editor: dates, location, description, type, links.
• Committee management: assign chairs / co-chairs / area leads via event_committee_assignments.
• Session scheduling: CRUD on event_sessions, presenter assignment via event_session_presenters, session_type selection.
• Attendance: import / record event_attendances rows with role (attendee, speaker, organizer, sponsor, volunteer).
• Sponsor wiring: link event_sponsorships to each event (depends on #1959 organizations).

Context

Foundation must ship first (#1956). Schema already supports nearly all of this — events, event_committee_areas, event_committee_assignments, event_sessions, event_session_types, event_session_presenters, event_attendances. Lots of UI work, modest schema additions.

Implementation Notes

• Policy: canEditEvent(actor, { eventId }) — staff+ OR chairedEventIds.has(eventId).
• "Approval" workflow is one of the few places we need a real status state machine; design carefully during its brainstorm.
• This subsystem likely couples to Communications (#1964) for attendee notifications — flag the dependency during brainstorm.

Begin with the required brainstorm and spec under docs/superpowers/specs/, after checking the Foundation dependency in #1956 and the organizations dependency in #1959. Review the existing events, committee, session, presenter, attendance, and sponsorship schema named in the issue. Done requires decomposed specs covering the admin event lifecycle, permissions, committee and session management, attendance, and sponsor wiring, with the Communications dependency flagged.