feat(agent): Agent 工作台 - 计划插话记忆、统一模型选择器并修复摘要与视频入库

将计划清单、运行中插话和个人记忆接入云端 Agent；全站模型选择器统一为左右二级菜单。画布摘要按预算截断不再整轮拒绝，首页视频未知宽高可入库。README 补充贡献者 morrow。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/internal/handler/api.go

@@ -15,8 +15,10 @@ func RegisterCanvasAPI(api *gin.RouterGroup, svc *service.Service) {
 	RegisterAppearanceRoutes(api, svc)
 	RegisterFeatureAvailabilityRoutes(api, svc)
 	RegisterAgentRoutes(api, svc)
+	RegisterAgentMemoryRoutes(api, svc)
 	RegisterResponseInterceptionRoutes(api, svc)
 	RegisterAdminRoutes(api, svc)
+	RegisterAgentLessonAdminRoutes(api, svc)
 	RegisterAdminAnalyticsRoutes(api, svc)
 	RegisterAdminStorageRoutes(api, svc)
 	RegisterAdminUpdateRoutes(api, svc)