fix: make evaluation form category migration fully idempotent

The migration partially applied (column added, then failed on DROP
CONSTRAINT). Make every statement idempotent with IF EXISTS / IF NOT
EXISTS so it can safely re-run after resolve --rolled-back.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

prisma/migrations/20260331000000_add_evaluation_form_category/migration.sql

@@ -1,18 +1,21 @@
 -- AlterTable: add nullable category column to EvaluationForm
-ALTER TABLE "EvaluationForm" ADD COLUMN "category" "CompetitionCategory";
+ALTER TABLE "EvaluationForm" ADD COLUMN IF NOT EXISTS "category" "CompetitionCategory";
 
 -- Drop old unique constraint (IF EXISTS — may not exist on fresh databases where
 -- the constraint was never created or was already removed by an earlier migration)
 ALTER TABLE "EvaluationForm" DROP CONSTRAINT IF EXISTS "EvaluationForm_roundId_version_key";
 
 -- Add new unique constraint including category
+ALTER TABLE "EvaluationForm" DROP CONSTRAINT IF EXISTS "EvaluationForm_roundId_version_category_key";
 ALTER TABLE "EvaluationForm" ADD CONSTRAINT "EvaluationForm_roundId_version_category_key" UNIQUE ("roundId", "version", "category");
 
 -- Partial unique index: prevent duplicate shared forms at the same version
 -- (PostgreSQL treats NULLs as distinct in unique constraints, so we need this)
+DROP INDEX IF EXISTS "EvaluationForm_roundId_version_null_category";
 CREATE UNIQUE INDEX "EvaluationForm_roundId_version_null_category"
   ON "EvaluationForm" ("roundId", "version") WHERE "category" IS NULL;
 
 -- Compound index for category-aware active form lookups
+DROP INDEX IF EXISTS "EvaluationForm_roundId_isActive_category_idx";
 CREATE INDEX "EvaluationForm_roundId_isActive_category_idx"
   ON "EvaluationForm" ("roundId", "isActive", "category");