feat: add tournamentType field to Event model

Add tournamentType field with default value 'individual':
- Supports 'individual' and 'team' tournament types
- Creates migration for database schema update

prisma/migrations/20260404012421_add_tournament_type/migration.sql

@@ -0,0 +1,2 @@
+-- AlterTable
+ALTER TABLE "events" ADD COLUMN     "tournamentType" TEXT NOT NULL DEFAULT 'individual';