feat(09-01): scaffold cert-manager module + shared node-forge helpers (GREEN)

- cert-manager.module.ts: OnModuleInit + seedCertManagerModule (CERT-06)
- cert-manager.seed.ts: slug='cert-manager', category='security-tools', isSystem=true
- cert-manager.service.ts: detectFormat, toForgeBuffer, getFingerprint, parsePemChain;
  operation stubs parseCert/splitCerts/mergeCerts/convertCert throw NotImplementedException
- cert-manager.controller.ts: 4 POST routes with FileInterceptor/FilesInterceptor
  (5 MB limit each), @UseModule('cert-manager') guard, BadRequestException on missing input
- dto/: ParseCertDto, MergeCertsDto, ConvertCertDto
- app.module.ts: CertManagerModule added to imports array
- All 11 Vitest tests pass; type-check clean

apps/api/src/app.module.ts

@@ -12,6 +12,7 @@ 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 { CertManagerModule } from './cert-manager/cert-manager.module';
 import { DomaincheckModule } from './domaincheck/domaincheck.module';
 import { ModuleRegistryModule } from './module-registry/module-registry.module';
 import { PrismaModule } from './prisma/prisma.module';
@@ -33,6 +34,7 @@ import { UserModule } from './user/user.module';
     LdapModule,
     ModuleRegistryModule,
     DomaincheckModule,
+    CertManagerModule,
     DashboardModule,
     CalendarModule,
     SettingsModule,