refactor(timeline): 解耦机位片段与运镜关键帧并新增过渡片段编辑

- 新增 TransitionClipEditor 与 CameraClipEditor，支持编辑过渡类型、时长及机位片段起止
- 抽出可复用的 TimelineClipDragHandle，支持拖拽、修剪、吸附与方向键微调
- 机位轨道改用显式活跃片段（CameraActiveClip），关键帧仅作只读占位推导
- 画布视锥线支持机位自定义颜色
- 视频导出时传入过渡片段、机位与场景参数以保持预览一致
- 更新 TimelinePanel 相关测试以覆盖新模型与交互

src/editor/io/videoExport.ts

@@ -231,6 +231,7 @@ async function exportVideoFrameByFrame(view: VideoExportView): Promise<void> {
       const displayCameraId =
         view === "camera"
           ? getActiveCameraIdAtTime(
+              directorStore.project.timeline.transitionClips,
               directorStore.project.timeline.cameraTracks,
               directorStore.project.activeCameraId,
               time
@@ -239,7 +240,10 @@ async function exportVideoFrameByFrame(view: VideoExportView): Promise<void> {
       // 有运镜轨道时两边共用同一份插值（预览 / 导出一致）；返回 false 表示没覆盖相机
       const appliedCameraTrack = applyActiveCameraViewAtTime({
         camera: frameCamera,
+        transitionClips: directorStore.project.timeline.transitionClips,
         cameraTracks: directorStore.project.timeline.cameraTracks,
+        cameras: directorStore.project.cameras,
+        projectScene: directorStore.project.scene,
         activeCameraId: displayCameraId,
         playhead: time,
         viewMode: view,