修复统一创作页软键盘黑底

让统一创作页根容器保留平台背景并限制滚动穿透

让统一创作页内容区占满剩余高度，避免短表单露出宿主黑底

补充统一创作页回归测试、玩法链路文档和 Hermes 踩坑记录

src/components/unified-creation/UnifiedCreationPage.test.tsx

@@ -59,13 +59,15 @@ describe('UnifiedCreationPage', () => {
         .getByText('敲木鱼工作台')
         .closest('.unified-creation-page__content')
         ?.className,
-    ).toContain('min-h-max');
+    ).toContain('flex-1');
     expect(
       screen
         .getByText('敲木鱼工作台')
         .closest('.unified-creation-page__content')
         ?.className,
-    ).not.toContain('min-h-0');
+    ).toContain('min-h-0');
     expect(root?.className).toContain('overflow-y-auto');
+    expect(root?.className).toContain('overscroll-contain');
+    expect(root?.className).toContain('bg-[image:var(--platform-body-fill)]');
   });
 });

src/components/unified-creation/UnifiedCreationPage.tsx

@@ -18,7 +18,7 @@ export function UnifiedCreationPage({
 }: UnifiedCreationPageProps) {
   return (
     <div
-      className="unified-creation-page platform-remap-surface mx-auto flex h-full min-h-0 w-full max-w-5xl flex-col overflow-y-auto overflow-x-hidden px-3 pt-2 sm:px-4 sm:pt-3"
+      className="unified-creation-page platform-remap-surface mx-auto flex h-full min-h-0 w-full max-w-5xl flex-col overflow-y-auto overflow-x-hidden overscroll-contain bg-[image:var(--platform-body-fill)] px-3 pt-2 sm:px-4 sm:pt-3"
       data-play-id={spec.playId}
       data-field-kinds={spec.fields.map((field) => field.kind).join(',')}
       data-workspace-stage={spec.workspaceStage}
@@ -65,7 +65,7 @@ export function UnifiedCreationPage({
           ))}
         </ul>
       </div>
-      <div className="unified-creation-page__content flex min-h-max flex-col pb-3 sm:pb-4">
+      <div className="unified-creation-page__content flex min-h-0 flex-1 flex-col pb-3 sm:pb-4">
         {children}
       </div>
     </div>