fix: drop stale unique index blocking per-category evaluation forms

The category migration used DROP CONSTRAINT but the index was created
with CREATE UNIQUE INDEX, so it was never actually removed. This
prevented saving business concept criteria when startup criteria
already existed at the same version number.

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

prisma/migrations/20260410000000_fix_evaluation_form_unique_index/migration.sql

@@ -0,0 +1,5 @@
+-- Fix: the category migration used DROP CONSTRAINT to remove the old
+-- (roundId, version) uniqueness rule, but it was created as a UNIQUE INDEX
+-- (not a constraint) by an earlier migration, so it was never actually dropped.
+-- This blocks per-category forms from sharing a version number.
+DROP INDEX IF EXISTS "EvaluationForm_roundId_version_key";