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>

src/server/routers/mentor.ts

@@ -1057,7 +1057,7 @@ export const mentorRouter = router({
           userId: ctx.user.id,
           action: 'COMPLETE_MILESTONE',
           entityType: 'MentorMilestoneCompletion',
-          entityId: `${completion.milestoneId}_${completion.mentorAssignmentId}`,
+          entityId: completion.id,
           detailsJson: {
             milestoneId: input.milestoneId,
             mentorAssignmentId: input.mentorAssignmentId,