Fix zulip 12.x env vars, try open-webui v0.10.0 intermediate upgrade

- zulip: rename legacy env vars per 12.x migration guide
  (DB_HOST -> SETTING_REMOTE_POSTGRES_HOST, etc.)
  Remove DISABLE_HTTPS/SSL_CERTIFICATE_GENERATION (HTTP is default in 12.x)
  Re-enable slot 12 as latest
- open-webui: try v0.10.0 as intermediate step from v0.9.5
  (v0.12.4 had duplicate column migration error jumping from v0.9.5)

open-webui/versions/0/deployment.yaml

@@ -19,7 +19,7 @@ spec:
           type: RuntimeDefault
       containers:
       - name: open-webui
-        image: ghcr.io/open-webui/open-webui:v0.9.5
+        image: ghcr.io/open-webui/open-webui:v0.10.0
         imagePullPolicy: IfNotPresent
         securityContext:
           allowPrivilegeEscalation: false

open-webui/versions/0/manifest.yaml

@@ -1,4 +1,4 @@
-version: 0.9.5-5
+version: 0.10.0
 defaultConfig:
   namespace: open-webui
   storage: 2Gi