fix(infra): Stalwart v0.16 management admin is a real account (admin@dezky.eu)

The v0.16 config migration silently dropped the fallback admin — the live
server had ZERO accounts, so every platform-api JMAP call 401'd and tenant
mail provisioning was dead. Bootstrapped via recovery mode on node1
(STALWART_RECOVERY_ADMIN): created the dezky.eu domain + an admin account
with the Admin role and the existing STALWART_ADMIN_PASSWORD.

v0.16 logins use the full address, so STALWART_ADMIN_USER becomes
admin@dezky.eu; config-rev annotation bump rolls platform-api so it picks
up the new env. install.sh follow-ups now document the recovery-mode
bootstrap for rebuilds instead of the defunct fallback-admin promise.

infrastructure/production/fleet/apps/platform-api.yaml

@@ -18,6 +18,10 @@ spec:
     metadata:
       labels:
         app.kubernetes.io/name: platform-api
+      annotations:
+        # Bump to force a rolling restart when only the ConfigMap changed —
+        # pods read it as env, which is only resolved at container start.
+        dezky.eu/config-rev: "2"
     spec:
       containers:
         - name: platform-api