Updates for performance issues seen by picachui on COMPLETED challenges request (PM-2206)

Author: jmgasper

prisma/migrations/20251130100000_add_challenge_groups_gin_index/migration.sql

@@ -0,0 +1,4 @@
+-- Improve search responsiveness for group-constrained queries
+CREATE INDEX IF NOT EXISTS "challenge_groups_gin_idx"
+  ON "challenges"."Challenge"
+  USING GIN ("groups");

prisma/schema.prisma

@@ -148,6 +148,7 @@ model Challenge {
   @@index([updatedAt])
   @@index([typeId])
   @@index([trackId])
+  @@index([groups], type: Gin, map: "challenge_groups_gin_idx")
   @@index([submissionStartDate])
   @@index([submissionEndDate])
   @@index([registrationStartDate])