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/components/VideoWorkspace.tsx

@@ -5,10 +5,12 @@ import {
   buildAnnotationPayload,
   deleteAnnotation,
   exportCoco,
+  exportMasks,
   getProjectAnnotations,
   getProjectFrames,
   getTask,
   getTemplates,
+  importGtMask,
   parseMedia,
   saveAnnotation,
   updateAnnotation,
@@ -25,18 +27,24 @@ function sleep(ms: number) {
 }
 
 export function VideoWorkspace({ onNavigateToAI }: { onNavigateToAI?: () => void }) {
+  const gtMaskInputRef = React.useRef<HTMLInputElement>(null);
   const activeTool = useStore((state) => state.activeTool);
   const setActiveTool = useStore((state) => state.setActiveTool);
   const currentProject = useStore((state) => state.currentProject);
   const frames = useStore((state) => state.frames);
   const currentFrameIndex = useStore((state) => state.currentFrameIndex);
   const masks = useStore((state) => state.masks);
+  const maskHistory = useStore((state) => state.maskHistory);
+  const maskFuture = useStore((state) => state.maskFuture);
   const activeTemplateId = useStore((state) => state.activeTemplateId);
   const setFrames = useStore((state) => state.setFrames);
   const setCurrentFrame = useStore((state) => state.setCurrentFrame);
   const setMasks = useStore((state) => state.setMasks);
+  const undoMasks = useStore((state) => state.undoMasks);
+  const redoMasks = useStore((state) => state.redoMasks);
   const [isSaving, setIsSaving] = useState(false);
   const [isExporting, setIsExporting] = useState(false);
+  const [isImportingGt, setIsImportingGt] = useState(false);
   const [statusMessage, setStatusMessage] = useState('');
 
   const hydrateSavedAnnotations = useCallback(async (projectId: string, projectFrames: Frame[]) => {
@@ -216,6 +224,18 @@ export function VideoWorkspace({ onNavigateToAI }: { onNavigateToAI?: () => void
     }
   }, [currentFrame, masks, setMasks]);
 
+  const handleDeleteMaskAnnotations = useCallback(async (annotationIds: string[]) => {
+    if (annotationIds.length === 0) return;
+    try {
+      await Promise.all(annotationIds.map((annotationId) => deleteAnnotation(annotationId)));
+      setStatusMessage(`已删除 ${annotationIds.length} 个被合并标注`);
+    } catch (err) {
+      console.error('Delete merged annotations failed:', err);
+      setStatusMessage('合并后删除原标注失败，请检查后端服务');
+      throw err;
+    }
+  }, []);
+
   const handleSave = async () => {
     try {
       await savePendingAnnotations();
@@ -248,6 +268,52 @@ export function VideoWorkspace({ onNavigateToAI }: { onNavigateToAI?: () => void
     }
   };
 
+  const downloadBlob = (blob: Blob, filename: string) => {
+    const url = URL.createObjectURL(blob);
+    const link = document.createElement('a');
+    link.href = url;
+    link.download = filename;
+    document.body.appendChild(link);
+    link.click();
+    link.remove();
+    URL.revokeObjectURL(url);
+  };
+
+  const handleExportMasks = async () => {
+    if (!currentProject?.id) return;
+    setIsExporting(true);
+    setStatusMessage('正在准备导出语义 Mask ZIP...');
+    try {
+      await savePendingAnnotations({ silent: true });
+      const blob = await exportMasks(currentProject.id);
+      downloadBlob(blob, `project_${currentProject.id}_masks.zip`);
+      setStatusMessage('PNG Mask ZIP 已导出');
+    } catch (err) {
+      console.error('Mask export failed:', err);
+      setStatusMessage('Mask 导出失败，请检查后端服务');
+    } finally {
+      setIsExporting(false);
+    }
+  };
+
+  const handleImportGtMask = async (event: React.ChangeEvent<HTMLInputElement>) => {
+    const file = event.target.files?.[0];
+    if (!file || !currentProject?.id || !currentFrame?.id) return;
+    setIsImportingGt(true);
+    setStatusMessage('正在导入 GT Mask...');
+    try {
+      const imported = await importGtMask(file, currentProject.id, currentFrame.id);
+      await hydrateSavedAnnotations(currentProject.id, frames);
+      setStatusMessage(`已导入 ${imported.length} 个 GT 区域`);
+    } catch (err) {
+      console.error('GT mask import failed:', err);
+      setStatusMessage('GT Mask 导入失败，请检查文件或后端服务');
+    } finally {
+      setIsImportingGt(false);
+      event.target.value = '';
+    }
+  };
+
   return (
     <div className="w-full h-full flex flex-col bg-[#0a0a0a]">
       {/* Top Header / Status bar */}
@@ -264,6 +330,27 @@ export function VideoWorkspace({ onNavigateToAI }: { onNavigateToAI?: () => void
             </span>
           )}
           <ModelStatusBadge />
+          <input
+            ref={gtMaskInputRef}
+            type="file"
+            accept="image/png,image/jpeg,image/bmp,image/tiff"
+            className="hidden"
+            onChange={handleImportGtMask}
+          />
+          <button
+            onClick={() => gtMaskInputRef.current?.click()}
+            disabled={!currentProject?.id || !currentFrame?.id || isImportingGt || isSaving || isExporting}
+            className="px-4 py-1.5 bg-white/5 hover:bg-white/10 border border-white/10 rounded-md text-xs transition-colors text-white disabled:opacity-40 disabled:cursor-not-allowed"
+          >
+            {isImportingGt ? '导入中...' : '导入 GT Mask'}
+          </button>
+          <button
+            onClick={handleExportMasks}
+            disabled={!currentProject?.id || isExporting || isSaving}
+            className="px-4 py-1.5 bg-white/5 hover:bg-white/10 border border-white/10 rounded-md text-xs transition-colors text-white disabled:opacity-40 disabled:cursor-not-allowed"
+          >
+            {isExporting ? '导出中...' : '导出 PNG Mask ZIP'}
+          </button>
           <button
             onClick={handleExport}
             disabled={!currentProject?.id || isExporting || isSaving}
@@ -283,11 +370,24 @@ export function VideoWorkspace({ onNavigateToAI }: { onNavigateToAI?: () => void
 
       {/* Main Workspace Area */}
       <div className="flex-1 flex overflow-hidden">
-        <ToolsPalette activeTool={activeTool} setActiveTool={setActiveTool} onTriggerAI={onNavigateToAI} />
+        <ToolsPalette
+          activeTool={activeTool}
+          setActiveTool={setActiveTool}
+          onTriggerAI={onNavigateToAI}
+          onUndo={undoMasks}
+          onRedo={redoMasks}
+          canUndo={maskHistory.length > 0}
+          canRedo={maskFuture.length > 0}
+        />
         
         <div className="flex-1 relative flex items-center justify-center p-8 bg-[#151515] overflow-hidden">
           <div className="relative w-full h-full bg-[#1e1e1e] border border-white/5 shadow-2xl rounded-sm">
-            <CanvasArea activeTool={activeTool} frame={currentFrame} onClearMasks={handleClearCurrentFrameMasks} />
+            <CanvasArea
+              activeTool={activeTool}
+              frame={currentFrame}
+              onClearMasks={handleClearCurrentFrameMasks}
+              onDeleteMaskAnnotations={handleDeleteMaskAnnotations}
+            />
           </div>
         </div>