feat: 加固运行期可靠性并补齐调度与观测接口

- 运行句柄按 run_id 归属，修复取消后重跑时闸门被旧运行删除的竞态
- 调度循环改用取消令牌退出，启动时对账遗留运行，校验 rows_affected
- 三类任务统一参与调度，新增 /api/v1/stats 与 /api/v1/schedule
- SQLite 启用 WAL 与 busy_timeout，日志清理跳过活跃文件，单行上限 256 KiB
- 前端缓存管理令牌并在 403 时重试一次，仪表盘改用统计接口

contracts/openapi.json

@@ -317,6 +317,29 @@
         }
       }
     },
+    "/api/v1/schedule": {
+      "get": {
+        "tags": [
+          "tasks"
+        ],
+        "operationId": "list_schedule",
+        "responses": {
+          "200": {
+            "description": "Next trigger time per enabled task",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "type": "array",
+                  "items": {
+                    "$ref": "#/components/schemas/ScheduledTaskResponse"
+                  }
+                }
+              }
+            }
+          }
+        }
+      }
+    },
     "/api/v1/session": {
       "get": {
         "tags": [
@@ -337,6 +360,26 @@
         }
       }
     },
+    "/api/v1/stats": {
+      "get": {
+        "tags": [
+          "tasks"
+        ],
+        "operationId": "task_stats",
+        "responses": {
+          "200": {
+            "description": "Dashboard counters",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/TaskStatsResponse"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
     "/api/v1/system/directories": {
       "get": {
         "tags": [
@@ -1088,6 +1131,26 @@
           "retry"
         ]
       },
+      "ScheduledTaskResponse": {
+        "type": "object",
+        "description": "已注册调度的任务及其下次触发时间。",
+        "required": [
+          "task_id"
+        ],
+        "properties": {
+          "next_run_at": {
+            "type": [
+              "string",
+              "null"
+            ],
+            "format": "date-time",
+            "description": "下次触发时间；调度正在重建时可能为空"
+          },
+          "task_id": {
+            "type": "string"
+          }
+        }
+      },
       "SessionResponse": {
         "type": "object",
         "required": [
@@ -1426,6 +1489,56 @@
           }
         }
       },
+      "TaskStatsResponse": {
+        "type": "object",
+        "description": "仪表盘指标：一次请求拿到全部计数，避免为每个指标各发一次列表查询。",
+        "required": [
+          "total",
+          "enabled",
+          "running",
+          "script",
+          "http",
+          "process"
+        ],
+        "properties": {
+          "enabled": {
+            "type": "integer",
+            "format": "int64",
+            "description": "已启用任务数",
+            "minimum": 0
+          },
+          "http": {
+            "type": "integer",
+            "format": "int64",
+            "description": "HTTP 类任务数",
+            "minimum": 0
+          },
+          "process": {
+            "type": "integer",
+            "format": "int64",
+            "description": "进程类任务数",
+            "minimum": 0
+          },
+          "running": {
+            "type": "integer",
+            "format": "int64",
+            "description": "当前正在执行的任务数",
+            "minimum": 0
+          },
+          "script": {
+            "type": "integer",
+            "format": "int64",
+            "description": "脚本类任务数",
+            "minimum": 0
+          },
+          "total": {
+            "type": "integer",
+            "format": "int64",
+            "description": "任务总数",
+            "minimum": 0
+          }
+        }
+      },
       "UpdateTaskRequest": {
         "type": "object",
         "required": [