refactor: tech debt batch 3 — type safety + assignment router split

#5 — Replaced 55x PrismaClient | any with proper Prisma types across 8 files
- Service files: PrismaClient | any → PrismaClient, tx: any → Prisma.TransactionClient
- Fixed 4 real bugs uncovered by typing:
  - mentor-workspace.ts: wrong FK fields (mentorAssignmentId → workspaceId, role → senderRole)
  - ai-shortlist.ts: untyped string passed to CompetitionCategory enum filter
  - result-lock.ts: unknown passed where Prisma.InputJsonValue required

#9 — Split assignment.ts (2,775 lines) into 6 focused files:
  - shared.ts (93 lines) — MOVABLE_EVAL_STATUSES, buildBatchNotifications, getCandidateJurors
  - assignment-crud.ts (473 lines) — 8 core CRUD procedures
  - assignment-suggestions.ts (880 lines) — AI suggestions + job runner
  - assignment-notifications.ts (138 lines) — 2 notification procedures
  - assignment-redistribution.ts (1,162 lines) — 8 reassign/transfer procedures
  - index.ts (15 lines) — barrel export with router merge, zero frontend changes

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

src/server/routers/applicant.ts

@@ -10,7 +10,7 @@ import { logAudit } from '@/server/utils/audit'
 import { createNotification } from '../services/in-app-notification'
 import { checkRequirementsAndTransition, triggerInProgressOnActivity, transitionProject, isTerminalState } from '../services/round-engine'
 import { EvaluationConfigSchema, MentoringConfigSchema } from '@/types/competition-configs'
-import type { Prisma, RoundType } from '@prisma/client'
+import type { PrismaClient, Prisma, RoundType } from '@prisma/client'
 
 // All uploads use the single configured bucket (MINIO_BUCKET / mopc-files).
 // Files are organized by path prefix: {ProjectName}/{RoundName}/... for submissions,
@@ -22,8 +22,7 @@ function generateInviteToken(): string {
 }
 
 /** Check if a project has been rejected in any round (based on ProjectRoundState, not Project.status) */
-// eslint-disable-next-line @typescript-eslint/no-explicit-any
-async function isProjectRejected(prisma: any, projectId: string): Promise<boolean> {
+async function isProjectRejected(prisma: PrismaClient, projectId: string): Promise<boolean> {
   const rejected = await prisma.projectRoundState.findFirst({
     where: { projectId, state: 'REJECTED' },
     select: { id: true },