feat: 重要通知模块、Server 酱独立配置与额度提醒

- 新增重要通知统一模块（邮件 + Server 酱）作为后台任务通知出口
- 拆出独立的 Server 酱 配置页（SendKey + Markdown 模板，支持 {title}/{body} 变量替换），通过仪表盘内置工具入口进入
- 新增提供商额度提醒后台 worker：余额低于阈值时通过重要通知推送，提供商配置页加入额度提醒开关与阈值
- 重要通知页加入配置可用性守卫：未配置任一通道时禁用总开关，未配置邮件/SendKey 时禁用对应通道开关
- 测试通知端点支持 channel 过滤（all/email/server_chan），并绕过总开关与通道开关，便于配置阶段先验证通道
- 修复：测试通知路由未在 buffered-body 白名单导致 channel 参数丢失、测试时邮件分支被误触发
- 修复：sub2api 验证响应中 username 为 null 时正确回退到 email，避免误报"验证响应缺少: 用户信息"

Co-Authored-By: Claude Opus 4.7 <[email protected]>

apps/aether-gateway/src/tests/control/admin/health_access.rs

@@ -754,6 +754,14 @@ async fn gateway_handles_admin_modules_status_locally_with_trusted_admin_princip
         .with_system_config_values_for_tests(vec![
             ("module.oauth.enabled".to_string(), json!(true)),
             ("module.management_tokens.enabled".to_string(), json!(true)),
+            (
+                "module.important_notification.email_enabled".to_string(),
+                json!(true),
+            ),
+            (
+                "module.important_notification.email_recipients".to_string(),
+                json!("[email protected]"),
+            ),
             ("smtp_host".to_string(), json!("smtp.example.com")),
             ("smtp_from_email".to_string(), json!("[email protected]")),
         ]);
@@ -796,9 +804,13 @@ async fn gateway_handles_admin_modules_status_locally_with_trusted_admin_princip
         "/admin/modules/chat-pii-redaction"
     );
     assert_eq!(
-        payload["notification_email"]["config_validated"],
+        payload["important_notification"]["config_validated"],
         json!(true)
     );
+    assert_eq!(
+        payload["important_notification"]["admin_route"],
+        "/admin/modules/important-notification"
+    );
     assert_eq!(*upstream_hits.lock().expect("mutex should lock"), 0);
 
     gateway_handle.abort();
@@ -828,6 +840,14 @@ async fn gateway_handles_admin_modules_status_locally_with_bearer_admin_session(
         .with_system_config_values_for_tests(vec![
             ("module.oauth.enabled".to_string(), json!(true)),
             ("module.management_tokens.enabled".to_string(), json!(true)),
+            (
+                "module.important_notification.email_enabled".to_string(),
+                json!(true),
+            ),
+            (
+                "module.important_notification.email_recipients".to_string(),
+                json!("[email protected]"),
+            ),
             ("smtp_host".to_string(), json!("smtp.example.com")),
             ("smtp_from_email".to_string(), json!("[email protected]")),
         ]);
@@ -855,7 +875,7 @@ async fn gateway_handles_admin_modules_status_locally_with_bearer_admin_session(
     assert_eq!(payload["oauth"]["config_validated"], json!(true));
     assert_eq!(payload["management_tokens"]["active"], json!(true));
     assert_eq!(
-        payload["notification_email"]["config_validated"],
+        payload["important_notification"]["config_validated"],
         json!(true)
     );
     assert_eq!(*upstream_hits.lock().expect("mutex should lock"), 0);