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>

src/types/competition.ts

@@ -5,7 +5,6 @@ import type {
   JuryGroupMember,
   SubmissionWindow,
   SubmissionFileRequirement,
-  AdvancementRule,
   RoundSubmissionVisibility,
   ProjectRoundState,
   DeliberationSession,
@@ -36,7 +35,6 @@ export type RoundSummary = Pick<
 export type RoundWithRelations = Round & {
   juryGroup: (JuryGroup & { members: JuryGroupMember[] }) | null
   submissionWindow: (SubmissionWindow & { fileRequirements: SubmissionFileRequirement[] }) | null
-  advancementRules: AdvancementRule[]
   visibleSubmissionWindows: (RoundSubmissionVisibility & { submissionWindow: SubmissionWindow })[]
   _count?: { projectRoundStates: number; assignments: number }
 }