feat(10-02): register TendersModule with marketplace self-seed + singleton poll config

- tenders.seed.ts seeds slug 'tender-radar' (isSystem: true, category 'procurement')
- tenders.module.ts self-seeds registry on boot (mirrors DkvModule pattern)
- upserts singleton doe-opendata TenderSourcePollConfig row (global, no forTenant())
- TendersModule added to app.module.ts imports

apps/api/src/tenders/tenders.seed.ts

@@ -0,0 +1,26 @@
+import { ModuleRegistryService } from '../module-registry/module-registry.service';
+
+/**
+ * Seeds the tender-radar module into the module registry.
+ *
+ * Called during TendersModule initialization to ensure the
+ * "tender-radar" module record exists in the database (CONFIG-01).
+ *
+ * isSystem: true registers the module in the registry but does NOT
+ * auto-activate it per tenant. Admin must activate via Marketplace UI.
+ */
+export async function seedTendersModule(
+  moduleRegistryService: ModuleRegistryService,
+): Promise<void> {
+  await moduleRegistryService.seedModule({
+    slug: 'tender-radar',
+    name: 'Ausschreibungs-Radar',
+    version: '1.0.0',
+    category: 'procurement',
+    description: {
+      de: 'Deutsche Ausschreibungen automatisch erfassen und durchsuchen',
+      en: 'Automatically track and search German public tenders',
+    },
+    isSystem: true,
+  });
+}