Add participant creation functionality to event API, including backend service and database integration. Update frontend to support participant registration and enhance UI for displaying registered players.

backend/migrations/005_guest_players.sql

@@ -0,0 +1,9 @@
+-- +mixmaker Up
+ALTER TABLE players
+    ALTER COLUMN account_id DROP NOT NULL;
+
+-- +mixmaker Down
+DELETE FROM rsvps WHERE player_id IN (SELECT id FROM players WHERE account_id IS NULL);
+DELETE FROM players WHERE account_id IS NULL;
+ALTER TABLE players
+    ALTER COLUMN account_id SET NOT NULL;