v0.3.5: restore full push notification system (14 channels)

Restored from v0.2.4:
- notifiers/: 14 push channels (bark/serverchan/telegram/lark/webhook/wechat/discord/smtp/...)
- push-user.service.ts: multi-user push config linked to cloud_configs.promotion_account
- notification.service.ts: full dispatcher with per-config + global fallback

New integrations:
- cloud.service.ts: notifyConfigEvent on save_success/cookie_expire/save_fail
- admin.routes.ts: 7 new API endpoints for push users, notify providers, channel test
- database.ts: migration for cloud_configs.notify_config column

How it works:
- Configure push channels in /admin/system-configs (global_notify_config JSON)
- Or per-cloud: link push_users.account = cloud_configs.promotion_account
- Notify events: save_success (green), cookie_expire (red), save_fail >=3 consecutive (yellow)

source_clean/src/cloud/notifiers/discord.notifier.ts

@@ -0,0 +1,38 @@
+import { Notifier, NotifyParams, NotifyResult, NotifierParam } from './notifier.types';
+
+const params: NotifierParam[] = [
+{ key: 'webhook_url', label: 'Webhook URL', type: 'url', required: true, placeholder: 'https://discord.com/api/webhooks/...' },
+    { key: 'title', label: '标题', type: 'text', default: 'CloudSearch', required: false },
+    { key: 'content', label: '内容', type: 'text', required: true },
+    { key: 'level', label: '级别', type: 'text', default: 'info', required: false },
+];
+
+export const discordNotifier: Notifier = {
+name: 'discord',
+    label: 'Discord',
+    params,
+    async notify(params) {
+        try {
+            const level = params.level || 'info';
+            const color = level === 'error' ? 0xff0000 : level === 'warn' ? 0xffa500 : 0x3498db;
+            const resp = await fetch(params.webhook_url, {
+                method: 'POST',
+                headers: { 'Content-Type': 'application/json' },
+                body: JSON.stringify({
+                    embeds: [{
+                            title: params.title || 'CloudSearch',
+                            description: params.content || '',
+                            color,
+                            footer: { text: 'CloudSearch \u00b7 ' + new Date().toLocaleString('zh-CN') },
+                        }],
+                }),
+            });
+            if (resp.ok)
+                return { success: true, message: 'Discord 推送成功' };
+            return { success: false, message: `HTTP ${resp.status}` };
+        }
+        catch (err: any) {
+            return { success: false, message: err.message };
+        }
+    },
+};