feat(matching): add schedule config for division collision groups

Allow event organizers to configure which divisions run in parallel
(same time slot) for accurate collision detection in the auto-matching
algorithm. Divisions in the same slot will collide with each other.

- Add scheduleConfig JSON field to Event model
- Add PUT /events/:slug/schedule-config API endpoint
- Update matching algorithm to use slot-based collision detection
- Add UI in EventDetailsPage for managing division slots
- Add unit tests for schedule-based collision detection

backend/prisma/migrations/20251123175317_add_schedule_config/migration.sql

@@ -0,0 +1,2 @@
+-- AlterTable
+ALTER TABLE "events" ADD COLUMN     "schedule_config" JSONB;