fix: Rate-Limit pro IPv6-/64 statt pro Einzeladresse

Der Standard-ThrottlerGuard trackt die volle req.ip. Ein IPv6-Client
kann innerhalb seines /64 beliebig Adressen rotieren und so die
Login-/Refresh-/SSO-Limits umgehen. Neuer ClientIpThrottlerGuard
liefert IPv4 unveraendert, IPv4-mapped als IPv4 und IPv6 als /64-Praefix.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

ApiCore-Backend/src/app.module.ts

@@ -1,7 +1,8 @@
 import { Module } from '@nestjs/common';
 import { ConfigModule } from '@nestjs/config';
 import { APP_GUARD, APP_INTERCEPTOR } from '@nestjs/core';
-import { ThrottlerGuard, ThrottlerModule } from '@nestjs/throttler';
+import { ThrottlerModule } from '@nestjs/throttler';
+import { ClientIpThrottlerGuard } from './common/throttler/client-ip-throttler.guard';
 import { ScheduleModule } from '@nestjs/schedule';
 import { PrismaModule } from './prisma/prisma.module';
 import { HealthModule } from './health/health.module';
@@ -112,7 +113,7 @@ import { IdempotencyCleanupService } from './common/idempotency/idempotency-clea
   providers: [
     // Throttle first: a request with a wrong token or API key must count
     // against the limit too, before any database lookup is spent on it.
-    { provide: APP_GUARD, useClass: ThrottlerGuard },
+    { provide: APP_GUARD, useClass: ClientIpThrottlerGuard },
     { provide: APP_GUARD, useClass: JwtAuthGuard },
     { provide: APP_GUARD, useClass: PermissionsGuard },
     { provide: APP_INTERCEPTOR, useClass: IdempotencyInterceptor },