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/tenants/provisioning.service.ts

@@ -35,13 +35,15 @@ export class ProvisioningService {
       tenant.authentikGroupId = String(group.pk)
     })
 
-    // Stalwart + OCIS are stubbed — the upstream call no-ops and we record the
-    // honest 'skipped' state by returning it from the step.
+    // Stalwart provisioning is real when STALWART_PROVISIONING_ENABLED is on;
+    // otherwise we record the honest 'skipped' state. ensureDomain is idempotent
+    // and auto-generates the domain's DKIM keys.
     await this.runStep(tenant, 'stalwart', async () => {
       const domain = this.domainFor(tenant.slug)
+      if (!this.stalwart.configured) return 'skipped'
       await this.stalwart.ensureDomain(domain, `Mail domain for tenant ${tenant.slug}`)
       tenant.stalwartDomain = domain
-      return 'skipped'
+      // falls through to 'ok' — a real upstream call succeeded
     })
 
     await this.runStep(tenant, 'ocis', async () => {