fix: security hardening + performance refactoring (code review batch 1)

- IDOR fix: deliberation vote now verifies juryMemberId === ctx.user.id
- Rate limiting: tRPC middleware (100/min), AI endpoints (5/hr), auth IP-based (10/15min)
- 6 compound indexes added to Prisma schema
- N+1 eliminated in processRoundClose (batch updateMany/createMany)
- N+1 eliminated in batchCheckRequirementsAndTransition (3 batch queries)
- Service extraction: juror-reassignment.ts (578 lines)
- Dead code removed: award.ts, cohort.ts, decision.ts (680 lines)
- 35 bare catch blocks replaced across 16 files
- Fire-and-forget async calls fixed
- Notification false positive bug fixed

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

src/server/routers/deliberation.ts

@@ -118,6 +118,14 @@ export const deliberationRouter = router({
       })
     )
     .mutation(async ({ ctx, input }) => {
+      // Enforce that jury members can only vote as themselves
+      if (input.juryMemberId !== ctx.user.id) {
+        throw new TRPCError({
+          code: 'FORBIDDEN',
+          message: 'You can only submit votes as yourself',
+        })
+      }
+
       const vote = await submitVote(input, ctx.prisma)
 
       await logAudit({