fix(db): make accentColor migration idempotent with IF NOT EXISTS

Column already existed in production DB — migration failed with 42701.
Hotfixed via psql UPDATE on _prisma_migrations; migration SQL updated
to prevent recurrence on fresh deploys.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/api/prisma/migrations/20260702000000_add_user_accent_color/migration.sql

@@ -1,2 +1,2 @@
 -- AlterTable
-ALTER TABLE "User" ADD COLUMN "accentColor" TEXT;
+ALTER TABLE "User" ADD COLUMN IF NOT EXISTS "accentColor" TEXT;