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/maintenance/mod.rs

@@ -7,8 +7,8 @@ pub(crate) use runtime::{
     ensure_provider_key_pool_scores_for_keys, inspect_proxy_upgrade_rollout,
     list_admin_cleanup_run_records, perform_account_self_check_once,
     perform_oauth_token_refresh_once, perform_pool_quota_probe_once, perform_provider_checkin_once,
-    pool_quota_probe_target_count, preview_manual_usage_cleanup, rebuild_admin_stats_once,
-    record_completed_cleanup_run, record_proxy_upgrade_traffic_success,
+    perform_provider_quota_alert_once, pool_quota_probe_target_count, preview_manual_usage_cleanup,
+    rebuild_admin_stats_once, record_completed_cleanup_run, record_proxy_upgrade_traffic_success,
     restore_proxy_upgrade_rollout_skipped_nodes, retry_proxy_upgrade_rollout_node,
     run_admin_system_cleanup_once, run_manual_usage_cleanup_once, skip_proxy_upgrade_rollout_node,
     spawn_account_self_check_worker, spawn_audit_cleanup_worker, spawn_db_maintenance_worker,
@@ -16,16 +16,17 @@ pub(crate) use runtime::{
     spawn_pending_cleanup_worker, spawn_pool_monitor_worker,
     spawn_pool_quota_probe_replenish_for_request, spawn_pool_quota_probe_worker,
     spawn_pool_score_rebuild_worker, spawn_provider_checkin_worker,
-    spawn_proxy_node_metrics_cleanup_worker, spawn_proxy_node_stale_cleanup_worker,
-    spawn_proxy_upgrade_rollout_worker, spawn_request_candidate_cleanup_worker,
-    spawn_stats_aggregation_worker, spawn_stats_hourly_aggregation_worker,
-    spawn_usage_cleanup_worker, spawn_wallet_daily_usage_aggregation_worker,
-    start_admin_request_body_cleanup_task, start_admin_system_purge_task,
-    start_manual_usage_cleanup_task, start_proxy_upgrade_rollout, AccountSelfCheckRunSummary,
-    AdminCleanupRunRecord, AdminCleanupTaskKind, AdminStatsRebuildSummary,
-    AdminSystemCleanupSummary, ManualUsageCleanupError, ManualUsageCleanupMode,
-    ManualUsageCleanupOptions, OAuthTokenRefreshRunSummary, PoolQuotaProbeRunSummary,
-    PoolQuotaProbeWorkerConfig, ProviderCheckinRunSummary, ProxyUpgradeRolloutCancelSummary,
+    spawn_provider_quota_alert_worker, spawn_proxy_node_metrics_cleanup_worker,
+    spawn_proxy_node_stale_cleanup_worker, spawn_proxy_upgrade_rollout_worker,
+    spawn_request_candidate_cleanup_worker, spawn_stats_aggregation_worker,
+    spawn_stats_hourly_aggregation_worker, spawn_usage_cleanup_worker,
+    spawn_wallet_daily_usage_aggregation_worker, start_admin_request_body_cleanup_task,
+    start_admin_system_purge_task, start_manual_usage_cleanup_task, start_proxy_upgrade_rollout,
+    AccountSelfCheckRunSummary, AdminCleanupRunRecord, AdminCleanupTaskKind,
+    AdminStatsRebuildSummary, AdminSystemCleanupSummary, ManualUsageCleanupError,
+    ManualUsageCleanupMode, ManualUsageCleanupOptions, OAuthTokenRefreshRunSummary,
+    PoolQuotaProbeRunSummary, PoolQuotaProbeWorkerConfig, ProviderCheckinRunSummary,
+    ProviderQuotaAlertRunSummary, ProxyUpgradeRolloutCancelSummary,
     ProxyUpgradeRolloutConflictClearSummary, ProxyUpgradeRolloutNodeActionSummary,
     ProxyUpgradeRolloutProbeConfig, ProxyUpgradeRolloutSkippedRestoreSummary,
     ProxyUpgradeRolloutStatus, ProxyUpgradeRolloutTrackedNodeState,