fix(db): 会话列表按 updated_at 再按 id 排

兼容层 order() 改为追加，不再只留最后一键。
GET /api/sessions 与套餐列表的两次 order() 都会进 SQL。

frontend/src/lib/db/local-postgres-client-core.ts

@@ -39,6 +39,15 @@ function identifier(value: string): string {
   return `"${normalized}"`;
 }
 
+export function formatOrderClause(
+  ordering: readonly { column: string; ascending: boolean }[],
+): string {
+  if (ordering.length === 0) return "";
+  return ` order by ${ordering
+    .map((item) => `${identifier(item.column)} ${item.ascending ? "asc" : "desc"}`)
+    .join(", ")}`;
+}
+
 export function upsertConflictColumns(options?: { onConflict?: string }): string[] {
   return (options?.onConflict ?? "")
     .split(",")
@@ -184,8 +193,7 @@ class LocalPostgresQueryBuilder implements PromiseLike<QueryResult> {
   private selectedColumns: string[] | null = null;
   private mutation: Mutation | null = null;
   private readonly filters: Filter[] = [];
-  private ordering: Readonly<{ column: string; ascending: boolean }> | null =
-    null;
+  private ordering: Array<{ column: string; ascending: boolean }> = [];
   private rowLimit: number | null = null;
   private abort: AbortSignal | null = null;
   private cardinality: "many" | "single" | "maybeSingle" = "many";
@@ -289,7 +297,7 @@ class LocalPostgresQueryBuilder implements PromiseLike<QueryResult> {
 
   order(column: string, options: { ascending?: boolean } = {}) {
     identifier(column);
-    this.ordering = { column, ascending: options.ascending !== false };
+    this.ordering.push({ column, ascending: options.ascending !== false });
     return this;
   }
 
@@ -389,9 +397,7 @@ class LocalPostgresQueryBuilder implements PromiseLike<QueryResult> {
               .join(", ");
             sql = `select ${selected} from public.${identifier(this.table)}`;
             sql += this.filterClause(parameters, types);
-            if (this.ordering) {
-              sql += ` order by ${identifier(this.ordering.column)} ${this.ordering.ascending ? "asc" : "desc"}`;
-            }
+            sql += formatOrderClause(this.ordering);
             if (this.rowLimit !== null) sql += ` limit ${this.rowLimit}`;
           } else if (
             this.mutation.kind === "insert" ||