refactor: tech debt batch 2 — drop dead models, stale columns, schema cleanup

Schema:
- Drop 4 dead models: OverrideAction, NotificationPolicy, AssignmentException, AdvancementRule
- Drop 2 dead enums: OverrideReasonCode, AdvancementRuleType
- Drop 3 stale columns: Project.roundId, ConflictOfInterest.roundId, Evaluation.version
- Remove 3 back-relation fields from User, Assignment, Round

Code:
- Fix 6 COI queries in assignment.ts + 1 in juror-reassignment.ts
  (roundId filter → assignment.roundId after column drop)
- Remove orphaned Project.roundId write in project.ts createProject
- Remove advancementRules include from round.ts getById
- Remove AdvancementRule from RoundWithRelations type
- Clean up seed.ts (remove advancement rule seeding)
- Clean up tests/helpers.ts (remove dead model cleanup)
- Add TODO comments on user delete mutations (FK violation risk)

Migration: 20260308000000_drop_dead_models_and_stale_columns

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

prisma/seed.ts

@@ -15,7 +15,6 @@ import {
   RoundStatus,
   CapMode,
   JuryGroupMemberRole,
-  AdvancementRuleType,
 } from '@prisma/client'
 import bcrypt from 'bcryptjs'
 // Inline default configs so seed has ZERO dependency on src/ (not available in Docker prod image)
@@ -858,24 +857,6 @@ async function main() {
   }
   console.log(`   ✓ ${rounds.length} rounds created (R1-R8)`)
 
-  // --- Advancement Rules (auto-advance between rounds) ---
-  for (let i = 0; i < rounds.length - 1; i++) {
-    await prisma.advancementRule.upsert({
-      where: {
-        roundId_sortOrder: { roundId: rounds[i].id, sortOrder: 0 },
-      },
-      update: {},
-      create: {
-        roundId: rounds[i].id,
-        ruleType: AdvancementRuleType.AUTO_ADVANCE,
-        sortOrder: 0,
-        targetRoundId: rounds[i + 1].id,
-        configJson: {},
-      },
-    })
-  }
-  console.log(`   ✓ ${rounds.length - 1} advancement rules created`)
-
   // --- Assign all projects to intake round (COMPLETED, since intake is closed) ---
   const intakeRound = rounds[0]
   const allProjects = await prisma.project.findMany({