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)

zulip/versions/12/deployment.yaml

@@ -37,21 +37,19 @@ spec:
                   key: adminPassword
             - name: SETTING_EXTERNAL_HOST
               value: "{{ .domain }}"
-            - name: SSL_CERTIFICATE_GENERATION
-              value: "self-signed"
             - name: SECRETS_secret_key
               valueFrom:
                 secretKeyRef:
                   name: zulip-secrets
                   key: secretKey
             # Database
-            - name: DB_HOST
+            - name: SETTING_REMOTE_POSTGRES_HOST
               value: "{{ .db.host }}"
-            - name: DB_HOST_PORT
+            - name: SETTING_REMOTE_POSTGRES_PORT
               value: "{{ .db.port }}"
-            - name: DB_NAME
+            - name: CONFIG_postgresql__database_name
               value: "{{ .db.name }}"
-            - name: DB_USER
+            - name: CONFIG_postgresql__database_user
               value: "{{ .db.user }}"
             - name: SECRETS_postgres_password
               valueFrom:
@@ -98,8 +96,6 @@ spec:
                   name: zulip-secrets
                   key: smtp.password
             # Reverse proxy configuration (Traefik terminates TLS)
-            - name: DISABLE_HTTPS
-              value: "true"
             - name: LOADBALANCER_IPS
               value: "10.244.0.0/16"
           resources: