feat(platform): real email domains, mailboxes & member lifecycle

Wire the mail/identity stack to real Stalwart/Authentik/OCIS provisioning,
replacing the mocked Domains and Users pages.

Domains (customer-admin):
- StalwartClient: real JMAP management (v0.16 dropped REST) — create/list/delete
  email domains via x:Domain at the internal http://stalwart:8080 listener;
  DKIM auto-generated; the records to publish are read from the domain's
  dnsZoneFile. Gated by STALWART_PROVISIONING_ENABLED.
- New Domain collection + DomainsModule: add/list/recheck/set-DMARC/remove,
  tenant-membership-gated and audited.
- DnsVerifierService: verifies MX/SPF/DKIM/DMARC/ownership against a public
  resolver (1.1.1.1/8.8.8.8) and diffs them against the expected records.
- Remove is guarded: refuses while accounts/aliases/mailing lists still use the
  domain (via Stalwart referential integrity).
- Domains page + add wizard on real data; sidebar badge counts domains needing
  attention.

Users & groups (customer-admin):
- Create a member provisioned across Authentik SSO, a Stalwart mailbox on the
  tenant's primary domain, and OCIS — returning a one-time password.
- Lifecycle: suspend/resume (Authentik is_active + freeze the mailbox via
  account permissions, original password preserved), force-logout (terminate
  sessions, filtered client-side so it can never end other users' sessions),
  reset password (new one-time password on SSO + mailbox), and remove (tear down
  mailbox + SSO identity + OCIS + doc; mailbox-in-use aware for multi-tenant
  users). Self-suspend / self-force-logout are blocked.

Infra: point platform-api at the internal Stalwart listener; document the new
STALWART_/provisioning vars in .env.example.

services/platform-api/src/app.module.ts

@@ -4,6 +4,7 @@ import { MongooseModule } from '@nestjs/mongoose'
 import { AuditModule } from './audit/audit.module.js'
 import { AuthModule } from './auth/auth.module.js'
 import { BillingModule } from './billing/billing.module.js'
+import { DomainsModule } from './domains/domains.module.js'
 import { FlagsModule } from './flags/flags.module.js'
 import { HealthModule } from './health/health.module.js'
 import { IngestModule } from './ingest/ingest.module.js'
@@ -25,6 +26,7 @@ import { UsersModule } from './users/users.module.js'
     AuditModule,
     HealthModule,
     TenantsModule,
+    DomainsModule,
     PartnersModule,
     UsersModule,
     MeModule,