Add event management features to API, including event cancellation, deletion, registration closure, and workflow balance generation. Introduce new roster management endpoints and enhance participant handling with avoided player preferences. Update database schema and service logic to support these changes.

backend/migrations/007_player_avoids.sql

@@ -0,0 +1,7 @@
+-- +mixmaker Up
+ALTER TABLE players
+    ADD COLUMN IF NOT EXISTS avoided_player_ids jsonb NOT NULL DEFAULT '[]'::jsonb;
+
+-- +mixmaker Down
+ALTER TABLE players
+    DROP COLUMN IF EXISTS avoided_player_ids;