Link event staffing shifts to ticketed events with auto pre-fill

Shift.ticketedEventId (nullable FK to TicketedEvent) persists the
link between a staffing shift and its parent event. The shift list
response now includes the linked event (id, slug, title, date) so
the admin UI can show context without a second request.

The Create/Edit Shift drawer gains a conditional Event picker that
only appears when kind is EVENT_STAFFING. Picking an event pre-fills
the form's date, startTime, endTime, and location (venue name +
address) — and seeds the title with "Staff: {event.title}" only if
the title field is still empty, so hand-typed overrides aren't
stomped. Switching kind away from EVENT_STAFFING clears the link.

The shifts table's Kind tag wraps in a tooltip showing the linked
event title when one is present, so organizers can see at a glance
which staffing shifts belong to which event without opening the
drawer.

Bunker Admin

api/prisma/migrations/20260411120000_shift_event_link/migration.sql

@@ -0,0 +1,7 @@
+
+-- AlterTable
+ALTER TABLE "shifts" ADD COLUMN     "ticketed_event_id" TEXT;
+
+-- AddForeignKey
+ALTER TABLE "shifts" ADD CONSTRAINT "shifts_ticketed_event_id_fkey" FOREIGN KEY ("ticketed_event_id") REFERENCES "ticketed_events"("id") ON DELETE SET NULL ON UPDATE CASCADE;
+