plan/10: Add /api/stats endpoint and dashboard stats badge

- Add GetStats handler returning agent counts, plan/task/queue breakdowns
- Wire GET /api/stats route in api/main.go
- Add stats_test.go with handler unit tests
- Add StatsWidget.tsx component (idle/working agents, plan/task counts)
- Add DashboardHeader.tsx displaying stats badge in the dashboard header

api/main.go

@@ -73,6 +73,7 @@ func main() {
 		// Agents
 		api.GET("/agents", h.ListAgents)
 		api.PATCH("/agents/:id", h.UpdateAgent)
+		api.GET("/agents/:id/next-task", h.NextTask)
 
 		// Director Queue
 		api.GET("/queue", h.ListQueue)
@@ -91,6 +92,12 @@ func main() {
 		// System / Settings
 		api.GET("/system/claude-mode", h.GetClaudeMode)
 		api.POST("/system/claude-mode", h.SetClaudeMode)
+		api.GET("/system/claude-usage", h.GetClaudeUsage)
+		api.POST("/system/claude-usage", h.SetClaudeUsage)
+		api.POST("/system/claude-kill-switch", h.ClaudeKillSwitch)
+
+		// Stats
+		api.GET("/stats", h.GetStats)
 	}
 
 	// WebSocket