feat(10-04): implement TenderSchedulerService — single global cron (poll-once-fan-out-many)

- One named cron job 'tender-doe-poll' for the whole platform; setInterval()
  takes no tenant argument (INGEST-06) — reuses DkvSchedulerService's
  CronJob require()-resolution + SchedulerRegistry mechanics, drops the
  per-tenant activeTenantId framing entirely
- onModuleInit() loads the singleton doe-opendata config via findUnique on
  the fixed sourceType slug, never findFirst (Pitfall D)
- Day-cursor gate stays inside TenderIngestionService.pollDueSources() —
  this scheduler only controls cron-tick frequency (Pitfall A separation)
- Registered in TendersModule.providers; ScheduleModule already global via
  AppModule, no re-registration needed

apps/api/src/tenders/tenders.module.ts

@@ -6,6 +6,7 @@ import { DoeOpenDataAdapter } from './adapters/doe-opendata.adapter';
 import { seedTendersModule } from './tenders.seed';
 import { TenderIngestionService } from './tender-ingestion.service';
 import { TenderNormalizerService } from './tender-normalizer.service';
+import { TenderSchedulerService } from './tender-scheduler.service';
 
 /**
  * NestJS module for the Ausschreibungs-Radar feature.
@@ -26,7 +27,12 @@ import { TenderNormalizerService } from './tender-normalizer.service';
 @Module({
   imports: [ModuleRegistryModule],
   controllers: [],
-  providers: [DoeOpenDataAdapter, TenderNormalizerService, TenderIngestionService],
+  providers: [
+    DoeOpenDataAdapter,
+    TenderNormalizerService,
+    TenderIngestionService,
+    TenderSchedulerService,
+  ],
 })
 export class TendersModule implements OnModuleInit {
   private readonly logger = new Logger(TendersModule.name);