docs: add system overview and plan-management-and-alert-remediation v1.3 design doc

- system-overview.md: full platform summary for NetMesh v2.x

- plan-management-and-alert-remediation.md: dual-track alert response design with 26 decisions

- alertRecordStore.cjs: remove auto_recover per D25 (alerts must be manually closed)

electron/bridges/inspection/alertRecordStore.cjs

@@ -116,14 +116,9 @@ function processAlert(readFn, writeFn, device, rule, metricValue, isTriggered) {
       _saveCounters(writeFn);
     }
 
-    // 有活跃告警 → 自动恢复（ACTIVE 和 ACKNOWLEDGED 都要恢复）
-    if (activeAlert && (activeAlert.status === ALERT_RECORD_STATUS.ACTIVE || activeAlert.status === ALERT_RECORD_STATUS.ACKNOWLEDGED)) {
-      activeAlert.status = ALERT_RECORD_STATUS.RESOLVED;
-      activeAlert.resolved_at = Date.now();
-      activeAlert.resolved_reason = "auto_recover";
-      _saveAlerts(writeFn);
-      return { ...activeAlert, action: "resolved" };
-    }
+    // 注意：不再自动恢复告警（auto_recover 已移除）。
+    // 告警一旦触发就保持 ACTIVE / ACKNOWLEDGED，必须由值班员手动 resolveAlert() 或 closeAlert() 才会关闭。
+    // 原因：闪断/偶发正常会导致告警"闪了一下就没了"，值班员还没来得及处理就消失了。
 
     return null;
   }