fix(db): add migration for User.accentColor column

Column was added to schema but migration was missing, causing
PrismaClientKnownRequestError P2022 on prod API startup.

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

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

@@ -0,0 +1,2 @@
+-- AlterTable
+ALTER TABLE "User" ADD COLUMN "accentColor" TEXT;