feat(flows): 新增流程编辑器基础功能与相关组件

feat(backend): 添加流程模型与服务支持
feat(frontend): 实现流程编辑器UI与交互
feat(assets): 添加流程节点图标资源
feat(plugins): 实现上下文菜单和运行时插件
feat(components): 新增基础节点和侧边栏组件
feat(routes): 添加流程相关路由配置
feat(models): 创建流程和运行日志数据模型
feat(services): 实现流程服务层逻辑
feat(migration): 添加流程相关数据库迁移
feat(config): 更新前端配置支持流程编辑器
feat(utils): 增强axios错误处理和工具函数

backend/flow_create.json

@@ -0,0 +1,3 @@
+{
+  "yaml": "# demo flow\nnodes:\n  - { id: start, kind: start, name: 开始 }\n  - { id: assign, kind: custom, name: 赋值, script: ctx.x = ctx.x + 1; }\n  - { id: cond, kind: custom, name: 条件 }\n  - { id: end, kind: end, name: 结束 }\nedges:\n  - { from: start, to: assign }\n  - { from: assign, to: cond }\n  - { from: cond, to: end, condition: ctx.x >= 1 }\n  - { from: cond, to: end }\n"
+}