feat: 看板全局时间筛选 + 协同留言抽屉

任务1 — 后端时间快照逻辑:
  get_dashboard_stats 新增 since/until 参数
  PENDING/WIP/总数 → 永远实时快照（忽略时间筛选）
  COMPLETED/REJECTED → 严格按时段过滤
  完成率基于过滤后的COMPLETED计算

任务2 — 前端时间筛选器:
  Radio.Button: 今天 | 近7天 | 近30天 | 自定义
  DatePicker.RangePicker 自定义区间
  切换时重新拉取 /dashboard/stats

任务3 — 协同留言抽屉:
  后端: GET /dashboard/messages（上帝视角全厂数据）
    JOIN Product → serial_number + material_name
    支持 keyword 搜: SN/物料名/留言人/内容
    按 created_at 倒序
  前端: Drawer + Input.Search + List
    点击"留言"数字打开抽屉
    分页展示: 留言人/内容/SN标签/物料名/时间

frontend/src/services/dashboardApi.ts

@@ -25,8 +25,25 @@ export interface WipTask {
   duration_hours: number;
 }
 
-export async function fetchDashboardStats(): Promise<DashboardStats> {
-  const { data } = await api.get<DashboardStats>("/dashboard/stats");
+export interface ProductMessageItem {
+  id: string;
+  content: string;
+  operator_name: string;
+  product_sn: string;
+  material_name: string;
+  created_at: string;
+}
+
+export interface ProductMessageList {
+  items: ProductMessageItem[];
+  total: number;
+}
+
+export async function fetchDashboardStats(since?: string, until?: string): Promise<DashboardStats> {
+  const params: Record<string, string> = {};
+  if (since) params.since = since;
+  if (until) params.until = until;
+  const { data } = await api.get<DashboardStats>("/dashboard/stats", { params });
   return data;
 }
 
@@ -34,3 +51,12 @@ export async function fetchWipTasks(limit = 20): Promise<WipTask[]> {
   const { data } = await api.get<WipTask[]>("/dashboard/wip-tasks", { params: { limit } });
   return data;
 }
+
+export async function fetchDashboardMessages(
+  keyword = "", skip = 0, limit = 30,
+): Promise<ProductMessageList> {
+  const { data } = await api.get<ProductMessageList>("/dashboard/messages", {
+    params: { keyword, skip, limit },
+  });
+  return data;
+}