feat(07-04): DkvModule + registry seed + AppModule registration + i18n keys

- dkv.seed.ts: seedDkvModule with slug=dkv-fleet, category=fleet, isSystem=true
- dkv.module.ts: imports ModuleRegistryModule + CalendarModule (CalendarCryptoService)
  provides all 7 DKV services + 2 providers + controller; OnModuleInit seeds registry
- app.module.ts: DkvModule added to imports (ScheduleModule + SettingsModule from Plans 01/03)
- de.json + en.json: complete dkvFleet namespace (50+ keys incl. status, col, form, errors)
- settings namespace extended with categoryGeneral, categorySmtp, smtp sub-object

apps/api/src/app.module.ts

@@ -11,6 +11,7 @@ import { LdapModule } from './ldap/ldap.module';
 import { MailModule } from './mail/mail.module';
 import { CalendarModule } from './calendar/calendar.module';
 import { DashboardModule } from './dashboard/dashboard.module';
+import { DkvModule } from './dkv/dkv.module';
 import { DomaincheckModule } from './domaincheck/domaincheck.module';
 import { ModuleRegistryModule } from './module-registry/module-registry.module';
 import { PrismaModule } from './prisma/prisma.module';
@@ -35,6 +36,7 @@ import { UserModule } from './user/user.module';
     DashboardModule,
     CalendarModule,
     SettingsModule,
+    DkvModule,
   ],
   providers: [
     // Global JWT guard: all routes require auth unless @Public()