checkpoint: stalwart deploy, beam-design, migration scripts, config tweaks

Stalwart + Bulwark mail server deployment with OIDC, TLS cert, vault
secrets. Beam design service. Pingora config cleanup. SeaweedFS
replication fix. Kratos values tweak. Migration scripts for mbox/messages
/calendars from La Suite to Stalwart.

base/stalwart/vault-secrets.yaml

@@ -0,0 +1,85 @@
+---
+apiVersion: secrets.hashicorp.com/v1beta1
+kind: VaultAuth
+metadata:
+  name: vso-auth
+  namespace: stalwart
+spec:
+  method: kubernetes
+  mount: kubernetes
+  kubernetes:
+    role: vso
+    serviceAccount: default
+---
+# Stalwart DB credentials from OpenBao database secrets engine (static role, 24h rotation).
+apiVersion: secrets.hashicorp.com/v1beta1
+kind: VaultDynamicSecret
+metadata:
+  name: stalwart-db-credentials
+  namespace: stalwart
+spec:
+  vaultAuthRef: vso-auth
+  mount: database
+  path: static-creds/stalwart
+  allowStaticCreds: true
+  refreshAfter: 5m
+  rolloutRestartTargets:
+    - kind: Deployment
+      name: stalwart
+  destination:
+    name: stalwart-db-credentials
+    create: true
+    overwrite: true
+    transformation:
+      excludeRaw: true
+      templates:
+        password:
+          text: "{{ index .Secrets \"password\" }}"
+---
+# Stalwart application secrets (admin password, DKIM key) from OpenBao KV.
+apiVersion: secrets.hashicorp.com/v1beta1
+kind: VaultStaticSecret
+metadata:
+  name: stalwart-app-secrets
+  namespace: stalwart
+spec:
+  vaultAuthRef: vso-auth
+  mount: secret
+  type: kv-v2
+  path: stalwart
+  refreshAfter: 30s
+  destination:
+    name: stalwart-app-secrets
+    create: true
+    overwrite: true
+    transformation:
+      excludeRaw: true
+      templates:
+        admin-password:
+          text: "{{ index .Secrets \"admin-password\" }}"
+        dkim-private-key:
+          text: "{{ index .Secrets \"dkim-private-key\" }}"
+---
+# SeaweedFS S3 credentials (shared — same secret as lasuite namespace).
+apiVersion: secrets.hashicorp.com/v1beta1
+kind: VaultStaticSecret
+metadata:
+  name: seaweedfs-s3-credentials
+  namespace: stalwart
+spec:
+  vaultAuthRef: vso-auth
+  mount: secret
+  type: kv-v2
+  path: seaweedfs
+  refreshAfter: 30s
+  destination:
+    name: seaweedfs-s3-credentials
+    create: true
+    overwrite: true
+    transformation:
+      excludeRaw: true
+      templates:
+        S3_ACCESS_KEY:
+          text: "{{ index .Secrets \"access-key\" }}"
+        S3_SECRET_KEY:
+          text: "{{ index .Secrets \"secret-key\" }}"