feat(integrations,classisland,server,web,desktop): ClassIsland 联动插件——上报课表与上课状态、下发提醒并回执、教室端推送通道

教室机器上的 ClassIsland 现在可以直接和班级小助手互通：插件走 /api/integrations/classisland/*，用设备令牌（X-ClassIsland-Token，库里只存 sha256）独立鉴权，不占用 JWT 通道。

- 服务端：新增 integrations 模块（上报 / 待弹出 / 回执 / 课表镜像 / 回写），两个迁移（设备令牌表、Class.notificationChannel）；通知、叫人、联动页下发统一复用 pushToClassIsland，避免"某个页面发的通知不联动"
- 插件：packages/classisland-plugin（.NET 8，独立于 pnpm workspace）——BridgeService 上报与提醒轮询、ScheduleMapper/ClassPlanWriter 课表镜像、Avalonia 设置页、ClassHelperNotificationProvider 在 ClassIsland 上弹出提醒；本地/内网地址强制直连，躲开系统代理返回的假 404
- 客户端：设置页可选提醒通道（both / client / classisland），并订阅相应实时事件
- Web 端：新增「ClassIsland 联动」页（设备管理与提醒下发）
- 校验与打包：verify:classisland（需后端）、verify:classisland-plugin（静态契约 54 项）、build/dist:classisland-plugin 产出 .cipx
- 文档：README 与 AGENTS.md 同步新增联动说明，docs/screenshots/classisland 留三张真机截图

门禁：pnpm lint 0 error、pnpm typecheck 四包通过、verify:classisland-plugin 54/54 通过。运行期仍需在装了 ClassIsland 的机器上实测（步骤见 AGENTS.md §8）。

packages/desktop-client/src/main/config.ts

@@ -1,7 +1,14 @@
 import fs from 'node:fs';
 import path from 'node:path';
 import { app, safeStorage } from 'electron';
-import { DEFAULT_ISLAND_APPEARANCE, DEFAULT_SERVER_URL, type IslandAppearance } from '@classhelper/shared';
+import {
+  CLASSISLAND_NOTIFICATION_CHANNELS,
+  DEFAULT_CLASSISLAND_NOTIFICATION_CHANNEL,
+  DEFAULT_ISLAND_APPEARANCE,
+  DEFAULT_SERVER_URL,
+  type ClassIslandNotificationChannel,
+  type IslandAppearance,
+} from '@classhelper/shared';
 import type { DesktopStoredConfig, HomeworkBoardSettings } from '../types/desktop.js';
 
 /** 作业页展示偏好默认值（看板 + 不显示时间 + 15px） */
@@ -22,6 +29,8 @@ interface PersistedConfig {
   island?: Partial<IslandAppearance>;
   /** 作业页展示偏好（向后兼容：旧配置文件没有该字段时用默认值补齐） */
   homeworkBoard?: Partial<HomeworkBoardSettings>;
+  /** 通知显示位置（向后兼容：旧配置文件没有该字段时按默认 both 补齐） */
+  notificationChannel?: ClassIslandNotificationChannel;
 }
 
 const DEFAULT_CONFIG: PersistedConfig = {
@@ -31,8 +40,18 @@ const DEFAULT_CONFIG: PersistedConfig = {
   tokenEncrypted: false,
   island: { ...DEFAULT_ISLAND_APPEARANCE },
   homeworkBoard: { ...DEFAULT_HOMEWORK_BOARD },
+  notificationChannel: DEFAULT_CLASSISLAND_NOTIFICATION_CHANNEL,
 };
 
+/** 通知显示位置的白名单校验：非法值一律回落到默认值，避免坏配置把提醒"静默吞掉" */
+function normalizeNotificationChannel(
+  input?: ClassIslandNotificationChannel,
+): ClassIslandNotificationChannel {
+  return CLASSISLAND_NOTIFICATION_CHANNELS.includes(input as ClassIslandNotificationChannel)
+    ? (input as ClassIslandNotificationChannel)
+    : DEFAULT_CLASSISLAND_NOTIFICATION_CHANNEL;
+}
+
 /** 作业页偏好的合法化（模式白名单、字号夹紧） */
 function normalizeHomeworkBoard(input?: Partial<HomeworkBoardSettings>): HomeworkBoardSettings {
   const mode = input?.mode === 'list' ? 'list' : 'board';
@@ -126,6 +145,7 @@ function readPersisted(): PersistedConfig {
       tokenEncrypted: parsed.tokenEncrypted === true,
       island: normalizeIslandAppearance(parsed.island),
       homeworkBoard: normalizeHomeworkBoard(parsed.homeworkBoard),
+      notificationChannel: normalizeNotificationChannel(parsed.notificationChannel),
     };
   } catch {
     return { ...DEFAULT_CONFIG };
@@ -147,6 +167,7 @@ export function getConfig(): DesktopStoredConfig {
     token: decryptToken(persisted),
     island: normalizeIslandAppearance(persisted.island),
     homeworkBoard: normalizeHomeworkBoard(persisted.homeworkBoard),
+    notificationChannel: normalizeNotificationChannel(persisted.notificationChannel),
   };
 }
 
@@ -169,6 +190,9 @@ export function saveConfig(patch: Partial<DesktopStoredConfig>): DesktopStoredCo
       ...patch.homeworkBoard,
     });
   }
+  if (patch.notificationChannel !== undefined) {
+    persisted.notificationChannel = normalizeNotificationChannel(patch.notificationChannel);
+  }
   if (patch.token !== undefined) {
     const encrypted = encryptToken(patch.token);
     persisted.token = encrypted.token;