Reconcile schema with migrations and fix failed migration

- Align schema.prisma with add_15_features migration (15 discrepancies):
  nullability, column names, PKs, missing/extra columns, onDelete behavior
- Make universal_apply_programid migration idempotent for safe re-execution
- Add reconciliation migration for missing FKs and indexes
- Fix message.ts and mentor.ts to match corrected schema field names

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

package.json

@@ -68,6 +68,7 @@
     "next": "^15.1.0",
     "next-auth": "^5.0.0-beta.25",
     "next-intl": "^4.8.2",
+    "next-themes": "^0.4.6",
     "nodemailer": "^7.0.7",
     "openai": "^6.16.0",
     "papaparse": "^5.4.1",