feat(admin): 运行时策略 - 配置对象存储策略与默认并发

backend/internal/platform/host.go

@@ -8,7 +8,7 @@ import (
 	"infinite-canvas/backend/internal/repository"
 )
 
-const TaskWorkerConcurrency = 3
+const TaskWorkerConcurrency = 8
 
 // Host 由组合根注入，避免 platform → app 回环。
 type Host interface {