feat(notify): 站内通知与手工开单，指派/改状态/评论/验收都有人收到

M2 最后一块：让"该我办了"能出现在系统里，并且允许不经过任务直接开单。

通知（backend/app/services/notify.py 统一出口）
- 七类触发：task_assigned、task_status_changed、item_commented、
  ticket_assigned、ticket_submitted、ticket_approved/rejected、task_unblocked
- 不通知自己：notify() 按 actor_id 跳过，调用方不用各自判断
- 已读：GET /notifications、/unread-count、POST /read、/read-all

手工开单
- POST /tickets：直接指定人、初始 open，与任务升级单共用同一条 kind='ticket' item，
  ticket_ext.parent_item_id 为空，验收通过不回流任务
- 指派前 _ensure_member 校验在册成员，越界指派返回 1001（避免"挂在看不到的名字上"）

前端
- Web：通知页 /w/:wsId/notifications（未读/全部，点开标已读并跳目标）；
  工单页"新建"面板；AppShell 每 30 秒对未读数，标已读后 dispatch notifications:changed 立刻刷新；
  任务与工单支持 ?open= 深链落地即展开
- 安卓：五个 tab 加"通知"，未读数 30 秒刷新；工单动作按需求人/办理人/管理员显隐；手工开单对话框

验证
- pytest 85 passed（新增 backend/tests/test_notifications.py 6 个用例）
- ruff check / format --check 全 0
- tsc --noEmit 通过；vite build 成功
- web/e2e/notifications.mjs 12 项断言全绿（手工开单 → B 收到 → 点开跳转 → 未读归零）
- 安卓：本机 JDK 25 与 Gradle 8.7 / AGP 8.7.3 不兼容，本次未做编译验证，
  装回 JDK 17 后第一件事是 assembleDebug

web/src/components/AppShell.tsx

@@ -6,6 +6,7 @@ import type { Workspace } from "../lib/types";
 import {
   Book,
   ChevronDown,
+  Bell,
   Columns,
   Inbox,
   Logo,
@@ -15,13 +16,25 @@ import {
   X,
 } from "./icons";
 
-export type Section = "tasks" | "board" | "tickets" | "knowledge" | "members";
+export type Section =
+  | "tasks"
+  | "board"
+  | "tickets"
+  | "knowledge"
+  | "notifications"
+  | "members";
 
 const NAV: { key: Section; label: string; to: (id: string) => string; icon: ReactNode }[] = [
   { key: "tasks", label: "任务", to: (id) => `/w/${id}`, icon: <Inbox size={16} /> },
   { key: "board", label: "看板", to: (id) => `/w/${id}/board`, icon: <Columns size={16} /> },
   { key: "tickets", label: "工单", to: (id) => `/w/${id}/tickets`, icon: <TicketIcon size={16} /> },
   { key: "knowledge", label: "知识", to: (id) => `/w/${id}/knowledge`, icon: <Book size={16} /> },
+  {
+    key: "notifications",
+    label: "通知",
+    to: (id) => `/w/${id}/notifications`,
+    icon: <Bell size={16} />,
+  },
   { key: "members", label: "成员", to: (id) => `/w/${id}/members`, icon: <Users size={16} /> },
 ];
 
@@ -73,16 +86,22 @@ export function AppShell({
     let alive = true;
     const load = async () => {
       try {
-        const r = await api.get<{ count: number }>(`/workspaces/${wsId}/notifications/unread-count`);
-        if (alive) setUnread(r.count);
+        const r = await api.get<{ unread: number }>(
+          `/workspaces/${wsId}/notifications/unread-count`,
+        );
+        if (alive) setUnread(r.unread ?? 0);
       } catch {
         /* 未读数失败不该影响主流程 */
       }
     };
+    // 通知页标了已读之后立刻刷新角标，不必等下一个轮询周期
+    const onChange = () => void load();
     void load();
+    window.addEventListener("notifications:changed", onChange);
     const timer = window.setInterval(load, 30_000);
     return () => {
       alive = false;
+      window.removeEventListener("notifications:changed", onChange);
       window.clearInterval(timer);
     };
   }, [wsId]);
@@ -174,7 +193,7 @@ export function AppShell({
               <Link key={n.key} to={n.to(ws.id)} className={`nav-item ${isActive ? "nav-item-active" : ""}`}>
                 <span className={isActive ? "text-primary-200" : "text-ink-400"}>{n.icon}</span>
                 {n.label}
-                {n.key === "tickets" && unread > 0 ? (
+                {n.key === "notifications" && unread > 0 ? (
                   <span
                     className={`ml-auto rounded-full px-1.5 py-px text-2xs font-semibold tabular-nums ${
                       isActive ? "bg-clay-500 text-white" : "bg-clay-500/12 text-clay-600"

web/src/components/icons.tsx

@@ -178,6 +178,13 @@ export const Inbox = (p: IconProps) => (
   </svg>
 );
 
+export const Bell = (p: IconProps) => (
+  <svg {...base(p)}>
+    <path d="M6 9a6 6 0 1 1 12 0c0 3.2.8 4.9 1.6 5.9.4.5 0 1.1-.6 1.1H5c-.6 0-1-.6-.6-1.1C5.2 13.9 6 12.2 6 9Z" />
+    <path d="M10 19a2 2 0 0 0 4 0" />
+  </svg>
+);
+
 export const Sparkle = (p: IconProps) => (
   <svg {...base(p)}>
     <path d="M12 3.5 13.6 9l5.4 1.6-5.4 1.6L12 17.5l-1.6-5.3L5 10.6 10.4 9Z" />