feat(canvas): 画布工作区 - 整合侧栏与风格预设并修复提示词回填

选择性整合 #547，保留主分支节点与工具条设计。新增默认折叠的节点、资产、任务和历史面板，风格与预设保留在节点内，移除重复入口。

补齐工具权限、提示词解析、资源引用保护及数据库迁移，修复提示词清空和连续编辑后的生成配置同步。

验证：前端全量 1925 项测试、构建、类型检查及 lint 通过；后端 go test ./... 通过。真实模型、PostgreSQL 实库与登录态页面验收仍待进行。

Refs #547

Co-authored-by: bensharp <bensharp@qq.com>

backend/internal/app/task_creation.go

@@ -44,6 +44,24 @@ func (s *Service) CreateTask(userID string, req CreateTaskRequest) (*model.Task,
 	if err != nil {
 		return nil, err
 	}
+	// Fail admission before queueing or charging; the worker validates again in
+	// case a tool is deleted or its visibility changes while queued.
+	toolMode, _ := normalizedInput["mode"].(string)
+	if toolMode == "" {
+		if strings.HasPrefix(taskType, "video_") || taskType == "canvas_video" {
+			toolMode = "video"
+		} else if taskType == "canvas_image" {
+			toolMode = "image"
+		}
+	}
+	if _, err := s.ResolveToolMentionTokens(userID, toolMode, prompt); err != nil {
+		return nil, err
+	}
+	if inputPrompt, ok := normalizedInput["prompt"].(string); ok && inputPrompt != prompt {
+		if _, err := s.ResolveToolMentionTokens(userID, toolMode, inputPrompt); err != nil {
+			return nil, err
+		}
+	}
 
 	var routed *RoutedModel
 	logicalModelID := strings.TrimSpace(req.LogicalModelID)