feat: 建立 SAM2 标注闭环基线

- 打通工作区真实标注闭环：支持手工多边形、矩形、圆形、点区域和线段生成 mask，并可保存、回显、更新和删除后端 annotation。

- 增强 polygon 编辑器：支持顶点拖动、顶点删除、边中点插入、多 polygon 子区域选择编辑，以及区域合并和区域去除。

- 接入 GT mask 导入：后端支持二值/多类别 mask 拆分、contour 转 polygon、distance transform seed point，前端支持导入、回显和 seed point 拖动编辑。

- 完善导出能力：COCO JSON 导出对齐前端，PNG mask ZIP 同时包含单标注 mask、按 zIndex 融合的 semantic_frame 和 semantic_classes.json。

- 打通异步任务管理：新增任务取消、重试、失败详情接口与 Dashboard 控件，worker 支持取消状态检查并通过 Redis/WebSocket 推送 cancelled 事件。

- 对接 Dashboard 后端数据：概览统计、解析队列和实时流转记录从 FastAPI 聚合接口与 WebSocket 更新。

- 增强 AI 推理参数：前端发送 crop_to_prompt、auto_filter_background 和 min_score，后端支持点/框 prompt 局部裁剪推理、结果回映射和负向点/低分过滤。

- 接入 SAM3 基础设施：新增独立 Python 3.12 sam3 环境安装脚本、外部 worker helper、后端桥接和真实 Python/CUDA/包/HF checkpoint access 状态检测。

- 保留 SAM3 授权边界：当前官方 facebook/sam3 gated 权重未授权时状态接口会返回不可用，不伪装成可推理。

- 增强前端状态管理：新增 mask undo/redo 历史栈、AI 模型选择状态、保存状态 dirty/draft/saved 流转和项目状态归一化。

- 更新前端 API 封装：补充 annotation CRUD、GT mask import、mask ZIP export、task cancel/retry/detail、AI runtime status 和 prediction options。

- 更新 UI 控件：ToolsPalette、AISegmentation、VideoWorkspace 和 CanvasArea 接入真实操作、导入导出、撤销重做、任务控制和模型状态。

- 新增 polygon-clipping 依赖，用于前端区域 union/difference 几何运算。

- 完善后端 schemas/status/progress：补充 AI 模型外部状态字段、任务 cancelled 状态和进度事件 payload。

- 补充测试覆盖：新增后端任务控制、SAM3 桥接、GT mask、导出融合、AI options 测试；补充前端 Canvas、Dashboard、VideoWorkspace、ToolsPalette、API 和 store 测试。

- 更新 README、AGENTS 和 doc 文档：冻结当前需求/设计/测试计划，标注真实功能、剩余 Mock、SAM3 授权边界和后续实施顺序。

src/store/useStore.ts

@@ -56,8 +56,10 @@ export interface Mask {
   color: string;
   opacity?: number;
   segmentation?: number[][];
+  points?: number[][];
   bbox?: [number, number, number, number];
   area?: number;
+  metadata?: Record<string, unknown>;
 }
 
 export interface Template {
@@ -110,6 +112,8 @@ export interface AppState {
   currentFrameIndex: number;
   annotations: Annotation[];
   masks: Mask[];
+  maskHistory: Mask[][];
+  maskFuture: Mask[][];
   setActiveModule: (module: string) => void;
   setActiveTool: (tool: string) => void;
   setAiModel: (model: AiModelId) => void;
@@ -120,6 +124,8 @@ export interface AppState {
   updateMask: (id: string, updates: Partial<Mask>) => void;
   setMasks: (masks: Mask[]) => void;
   clearMasks: () => void;
+  undoMasks: () => void;
+  redoMasks: () => void;
   removeAnnotation: (id: string) => void;
 
   // Templates
@@ -161,6 +167,8 @@ export const useStore = create<AppState>((set) => ({
       frames: [],
       annotations: [],
       masks: [],
+      maskHistory: [],
+      maskFuture: [],
       activeTemplateId: null,
       activeClassId: null,
       activeClass: null,
@@ -187,6 +195,8 @@ export const useStore = create<AppState>((set) => ({
   currentFrameIndex: 0,
   annotations: [],
   masks: [],
+  maskHistory: [],
+  maskFuture: [],
   setActiveModule: (activeModule: string) => set({ activeModule }),
   setActiveTool: (activeTool: string) => set({ activeTool }),
   setAiModel: (aiModel: AiModelId) => set({ aiModel }),
@@ -195,13 +205,54 @@ export const useStore = create<AppState>((set) => ({
   addAnnotation: (annotation: Annotation) =>
     set((state) => ({ annotations: [...state.annotations, annotation] })),
   addMask: (mask: Mask) =>
-    set((state) => ({ masks: [...state.masks, mask] })),
+    set((state) => ({
+      masks: [...state.masks, mask],
+      maskHistory: [...state.maskHistory, state.masks],
+      maskFuture: [],
+    })),
   updateMask: (id: string, updates: Partial<Mask>) =>
     set((state) => ({
       masks: state.masks.map((mask) => (mask.id === id ? { ...mask, ...updates } : mask)),
+      maskHistory: [...state.maskHistory, state.masks],
+      maskFuture: [],
     })),
-  setMasks: (masks: Mask[]) => set({ masks }),
-  clearMasks: () => set({ masks: [] }),
+  setMasks: (masks: Mask[]) =>
+    set((state) => {
+      const isInitialHydration = state.masks.length === 0
+        && state.maskHistory.length === 0
+        && state.maskFuture.length === 0;
+      return {
+        masks,
+        maskHistory: isInitialHydration ? [] : [...state.maskHistory, state.masks],
+        maskFuture: [],
+      };
+    }),
+  clearMasks: () =>
+    set((state) => ({
+      masks: [],
+      maskHistory: [...state.maskHistory, state.masks],
+      maskFuture: [],
+    })),
+  undoMasks: () =>
+    set((state) => {
+      if (state.maskHistory.length === 0) return state;
+      const previous = state.maskHistory[state.maskHistory.length - 1];
+      return {
+        masks: previous,
+        maskHistory: state.maskHistory.slice(0, -1),
+        maskFuture: [state.masks, ...state.maskFuture],
+      };
+    }),
+  redoMasks: () =>
+    set((state) => {
+      if (state.maskFuture.length === 0) return state;
+      const [next, ...rest] = state.maskFuture;
+      return {
+        masks: next,
+        maskHistory: [...state.maskHistory, state.masks],
+        maskFuture: rest,
+      };
+    }),
   removeAnnotation: (id: string) =>
     set((state) => ({
       annotations: state.annotations.filter((a) => a.id !== id),