fix(cluster): 收敛宁波单实例数据库拓扑

将生产 CNPG 固定为宁波单实例，并显式关闭旧同步复制配置。发布流程在拓扑收敛前校验主库位置并创建 OSS 备份，应用后验证单实例、无复制连接和主库可用。同步更新生产监控、集群验收和发布脚本回归测试。

deploy/kubernetes/easyai-ai-gateway-cluster-release

@@ -712,6 +712,65 @@ EOF
   return 1
 }
 
+prepare_postgres_single_instance() {
+  local source_sha=$1
+  local current_instances current_primary primary_node synchronous_enabled
+  if ! grep -Eq '^  instances: 1$' "$DESIRED_STATE_DIR/database.yaml" ||
+     ! grep -Eq '^    synchronous: null$' "$DESIRED_STATE_DIR/database.yaml"; then
+    echo 'production PostgreSQL desired state must declare one instance with synchronous replication disabled' >&2
+    return 1
+  fi
+  current_instances=$("${kubectl[@]}" get cluster easyai-postgres -n "$NAMESPACE" \
+    -o jsonpath='{.spec.instances}')
+  synchronous_enabled=$("${kubectl[@]}" get cluster easyai-postgres -n "$NAMESPACE" -o json |
+    jq -r '.spec.postgresql.synchronous != null')
+  if [[ $current_instances == 1 && $synchronous_enabled == false ]]; then
+    return 0
+  fi
+  current_primary=$("${kubectl[@]}" get cluster easyai-postgres -n "$NAMESPACE" \
+    -o jsonpath='{.status.currentPrimary}')
+  [[ $current_primary =~ ^easyai-postgres-[0-9]+$ ]] || {
+    echo "production PostgreSQL primary is unavailable: primary=${current_primary:-unknown}" >&2
+    return 1
+  }
+  primary_node=$("${kubectl[@]}" get pod "$current_primary" -n "$NAMESPACE" \
+    -o jsonpath='{.spec.nodeName}')
+  [[ $primary_node == easyai-ningbo ]] || {
+    echo "refusing PostgreSQL downscale while primary is outside Ningbo: primary=$current_primary node=$primary_node" >&2
+    return 1
+  }
+  run_backup "$source_sha"
+  # A distinct preflight field manager cannot remove the existing synchronous
+  # object by omission. Remove it explicitly before applying instances=1 so
+  # CNPG never validates the old number=1 setting against the new topology.
+  "${kubectl[@]}" patch cluster easyai-postgres -n "$NAMESPACE" --type=merge \
+    -p '{"spec":{"postgresql":{"synchronous":null}}}' >/dev/null
+}
+
+verify_postgres_single_instance() {
+  local state primary primary_node replicas
+  for _ in $(seq 1 120); do
+    state=$("${kubectl[@]}" get cluster easyai-postgres -n "$NAMESPACE" -o json |
+      jq -r '[.spec.instances, (.status.readyInstances // 0)] | @tsv')
+    if [[ $state == $'1\t1' ]]; then
+      primary=$("${kubectl[@]}" get cluster easyai-postgres -n "$NAMESPACE" \
+        -o jsonpath='{.status.currentPrimary}')
+      primary_node=$("${kubectl[@]}" get pod "$primary" -n "$NAMESPACE" \
+        -o jsonpath='{.spec.nodeName}')
+      replicas=$("${kubectl[@]}" exec -n "$NAMESPACE" "$primary" -c postgres -- \
+        psql -X -U postgres -d easyai_ai_gateway -At -c \
+        'SELECT count(*) FROM pg_stat_replication;' 2>/dev/null || true)
+      if [[ $primary_node == easyai-ningbo && $replicas == 0 ]]; then
+        echo "production_postgres=PASS topology=ningbo-single-instance primary=$primary"
+        return 0
+      fi
+    fi
+    sleep 5
+  done
+  echo "production PostgreSQL did not converge to Ningbo single-instance topology: state=${state:-unknown}" >&2
+  return 1
+}
+
 run_migrator() {
   local source_sha=$1
   local api_image=$2
@@ -929,6 +988,9 @@ activate_manifest() {
   deployment_snapshot=$(mktemp "$RELEASES_DIR/.deployments.XXXXXX")
   snapshot_application_deployments "$deployment_snapshot"
 
+  if [[ $action == deploy ]]; then
+    prepare_postgres_single_instance "$source_sha"
+  fi
   if [[ $action == deploy && $migrations_changed == true ]]; then
     run_backup "$source_sha"
     run_migrator "$source_sha" "$api_image"
@@ -943,6 +1005,12 @@ activate_manifest() {
     rm -f -- "$deployment_snapshot" "$current_file"
     return 1
   fi
+  if [[ $action == deploy ]] && ! verify_postgres_single_instance; then
+    echo '[cluster-release] PostgreSQL single-instance verification failed; restoring exact deployment snapshot' >&2
+    restore_application_deployments "$deployment_snapshot" || true
+    rm -f -- "$deployment_snapshot" "$current_file"
+    return 1
+  fi
   if [[ $action == deploy && $api_changed == true ]] &&
      ! run_capacity_controller_preflight "$source_sha" "$api_image"; then
     echo '[cluster-release] capacity controller preflight failed; restoring exact deployment snapshot' >&2