feat(tasks): 漏洞列改为按严重度分档显示 严/高/中/低

- TaskListMetricsAll 用 COUNT(*) FILTER 按 severity 分四档统计（同一条查询）
- TaskListMetrics.Findings 及 TaskDTO.findings 由数字改为 {critical,high,medium,low}
- 列表页「漏洞」列渲染 x/x/x/x，配色沿用 severity 语义、为 0 的档位弱化
- severity 为空/白名单外的记录不计入任一档；mock 同步为对象结构

web/src/lib/mock/data.ts

@@ -65,7 +65,7 @@ export const tasks: Task[] = [
     paused: false,
     active: true,
     in_flight: 3,
-    findings: 4,
+    findings: { critical: 1, high: 2, medium: 1, low: 0 },
     stalled: false,
     goals_total: 5,
     goals_met: 2,
@@ -91,7 +91,7 @@ export const tasks: Task[] = [
     paused: false,
     active: false,
     in_flight: 2,
-    findings: 2,
+    findings: { critical: 0, high: 1, medium: 1, low: 0 },
     stalled: false,
     goals_total: 4,
     goals_met: 1,

web/src/lib/mock/handler.ts

@@ -1192,7 +1192,7 @@ function route(m: string, path: string, seg: string[], q: URLSearchParams, b: Re
       paused: false,
       active: true,
       in_flight: 0,
-      findings: 0,
+      findings: { critical: 0, high: 0, medium: 0, low: 0 },
       stalled: false,
       goals_total: 0,
       goals_met: 0,

web/src/lib/types.ts

@@ -23,7 +23,7 @@ export interface Task {
   queued?: boolean;
   active?: boolean;
   in_flight?: number;
-  findings?: number; // 该任务已登记的漏洞数
+  findings?: { critical: number; high: number; medium: number; low: number }; // 已登记漏洞数(按严重度分档)
   last_activity?: string;
   stalled?: boolean;
   goals_total?: number;