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

server/server.go

@@ -148,7 +148,7 @@ func New(ctx context.Context, m *Manager, skillDir string, dataDir string, keyDi
 		chatCancel: map[string]context.CancelCauseFunc{}, triggerQ: map[string][]triggeredRun{},
 		triggerActive: map[string]int{}, triggerCfg: map[string]triggerBehavior{},
 		profChatAgents: map[int64]*agent.ChatAgent{},
-		provByProfile: map[int64]*provEntry{}, llmHealth: newLLMHealthRegistry(m.pg),
+		provByProfile:  map[int64]*provEntry{}, llmHealth: newLLMHealthRegistry(m.pg),
 		taskAgents: map[string]*taskAgentBundle{}, archiveWake: make(chan struct{}, 1)}
 	s.initSideQuestions()
 	// 熔断阈值/冷却是失败路径上的热参数，启动时把全局重试策略推给 Registry 一次；
@@ -1040,7 +1040,12 @@ func (s *Server) listTasks(w http.ResponseWriter, r *http.Request) {
 		dto.GoalsTotal = metric.Goals.Total
 		dto.GoalsMet = metric.Goals.Met
 		dto.InFlight = metric.RunningIntents
-		dto.Findings = metric.Findings
+		dto.Findings = FindingSeverityDTO{
+			Critical: metric.Findings.Critical,
+			High:     metric.Findings.High,
+			Medium:   metric.Findings.Medium,
+			Low:      metric.Findings.Low,
+		}
 		dtos = append(dtos, dto)
 	}
 	writeJSON(w, 200, map[string]any{"tasks": dtos, "active": active})