新增预览右键平移手势状态机

- 新增 previewRightPanGesture.ts：按下起手、按共用阈值判定是否进入平移、按起点全量 delta 复用 moveViewportFromPan 算视口
- 抬起裁决统一收口到 resolvePreviewRightPanRelease：平移过就只回视口，未平移且在预览内才按节点菜单处理
- shouldInterceptRightContextMenu 记录"按钮 2 且处于右键按下序列"的拦截窗口，兼容按下触发与抬起后触发的两类平台时序
- 新增 tests/previewRightPanGesture.test.ts 覆盖阈值边界、越阈值后不回弹、全量 delta、预览外抬起与拦截判据

验证：npx vitest run previewRightPanGesture.test.ts（5 passed）

apps/ai-game-creator-shell/src/view/ui-editor/components/preview/previewRightPanGesture.ts

@@ -0,0 +1,91 @@
+import {
+  type CanvasViewport,
+  createPanDragState,
+  type DragState,
+  moveViewportFromPan,
+} from '@genarrative/image-canvas-core';
+
+import {
+  passedDragThresholdScreen,
+  type ScreenPoint,
+} from './previewDragThreshold';
+
+/**
+ * 右键按下到抬起之间的手势状态。右键同时承载节点菜单与视图平移：
+ * 只有越过拖动阈值的移动才判定为平移，且一旦越阈值就不再回到"点击开菜单"。
+ */
+export type PreviewRightPanGesture = {
+  pointerId: number;
+  /** 按下点（屏幕坐标），平移按"按下点全量 delta"计算。 */
+  start: ScreenPoint;
+  panning: boolean;
+  pan: Extract<DragState, { kind: 'pan' }>;
+};
+
+export function createPreviewRightPanGesture({
+  pointerId,
+  pointer,
+  viewport,
+}: {
+  pointerId: number;
+  pointer: ScreenPoint;
+  viewport: CanvasViewport;
+}): PreviewRightPanGesture {
+  return {
+    pointerId,
+    start: pointer,
+    panning: false,
+    pan: createPanDragState({ pointerId, pointer, viewport }),
+  };
+}
+
+/** 未越阈值时原样返回同一个手势，避免无意义的重复状态写入。 */
+export function movePreviewRightPanGesture(
+  gesture: PreviewRightPanGesture,
+  pointer: ScreenPoint,
+): PreviewRightPanGesture {
+  if (gesture.panning || !passedDragThresholdScreen(gesture.start, pointer)) {
+    return gesture;
+  }
+  return { ...gesture, panning: true };
+}
+
+export type PreviewRightPanRelease = {
+  /** 平移后的视口；未判定为平移时为 null，调用方不要改视口。 */
+  viewport: CanvasViewport | null;
+  /** 是否按"节点右键菜单"处理。 */
+  openNodeMenu: boolean;
+};
+
+export function resolvePreviewRightPanRelease({
+  gesture,
+  pointer,
+  isInsidePreview,
+}: {
+  gesture: PreviewRightPanGesture;
+  pointer: ScreenPoint;
+  isInsidePreview: boolean;
+}): PreviewRightPanRelease {
+  return {
+    viewport: gesture.panning
+      ? moveViewportFromPan(gesture.pan, pointer)
+      : null,
+    openNodeMenu: !gesture.panning && isInsidePreview,
+  };
+}
+
+/**
+ * 预览是否接管这一次 contextmenu。
+ * 平台差异：Windows / Linux 的 Chromium 与 Firefox 在**按下**时触发 contextmenu，
+ * macOS 在指针抬起之后触发；而原生菜单一旦弹出，页面之后收不到 pointermove / pointerup，
+ * 所以必须按下时就拦截，并把拦截窗口保留到下一次指针按下之前。
+ */
+export function shouldInterceptRightContextMenu({
+  button,
+  withinRightPressSequence,
+}: {
+  button: number;
+  withinRightPressSequence: boolean;
+}): boolean {
+  return button === 2 && withinRightPressSequence;
+}

apps/ai-game-creator-shell/tests/previewRightPanGesture.test.ts

@@ -0,0 +1,100 @@
+import { describe, expect, it } from 'vitest';
+
+import {
+  createPreviewRightPanGesture,
+  movePreviewRightPanGesture,
+  resolvePreviewRightPanRelease,
+  shouldInterceptRightContextMenu,
+} from '../src/view/ui-editor/components/preview/previewRightPanGesture';
+
+const startViewport = { x: 10, y: -20, scale: 0.75 };
+
+function pressAt(x: number, y: number) {
+  return createPreviewRightPanGesture({
+    pointerId: 7,
+    pointer: { x, y },
+    viewport: startViewport,
+  });
+}
+
+describe('preview right-button pan gesture', () => {
+  it('starts as a click until the pointer passes the drag threshold', () => {
+    const gesture = pressAt(100, 100);
+
+    expect(gesture.panning).toBe(false);
+    expect(movePreviewRightPanGesture(gesture, { x: 101, y: 100 })).toBe(
+      gesture,
+    );
+    expect(
+      movePreviewRightPanGesture(gesture, { x: 102, y: 100 }).panning,
+    ).toBe(true);
+  });
+
+  it('keeps panning once engaged, even when the pointer returns to the start', () => {
+    const engaged = movePreviewRightPanGesture(pressAt(100, 100), {
+      x: 130,
+      y: 140,
+    });
+
+    expect(engaged.panning).toBe(true);
+    expect(
+      movePreviewRightPanGesture(engaged, { x: 100, y: 100 }).panning,
+    ).toBe(true);
+  });
+
+  it('pans by the full delta from the press point without touching the scale', () => {
+    const gesture = movePreviewRightPanGesture(pressAt(100, 100), {
+      x: 140,
+      y: 70,
+    });
+    const release = resolvePreviewRightPanRelease({
+      gesture,
+      pointer: { x: 140, y: 70 },
+      isInsidePreview: true,
+    });
+
+    expect(release.viewport).toEqual({ x: 50, y: -50, scale: 0.75 });
+    expect(release.openNodeMenu).toBe(false);
+  });
+
+  it('opens the node menu only for a clean release inside the preview', () => {
+    const gesture = pressAt(100, 100);
+
+    expect(
+      resolvePreviewRightPanRelease({
+        gesture,
+        pointer: { x: 101, y: 100 },
+        isInsidePreview: true,
+      }),
+    ).toEqual({ viewport: null, openNodeMenu: true });
+
+    expect(
+      resolvePreviewRightPanRelease({
+        gesture,
+        pointer: { x: 101, y: 100 },
+        isInsidePreview: false,
+      }),
+    ).toEqual({ viewport: null, openNodeMenu: false });
+  });
+
+  it('intercepts only the right button of the preview right-press sequence', () => {
+    expect(
+      shouldInterceptRightContextMenu({
+        button: 2,
+        withinRightPressSequence: true,
+      }),
+    ).toBe(true);
+    expect(
+      shouldInterceptRightContextMenu({
+        button: 2,
+        withinRightPressSequence: false,
+      }),
+    ).toBe(false);
+    expect(
+      shouldInterceptRightContextMenu({
+        button: 0,
+        withinRightPressSequence: true,
+      }),
+    ).toBe(false);
+  });
+});