修复移动端软键盘页面弹跳黑底

移除 H5 软键盘打开时平台壳全局 transform 位移，避免浏览器原生避让后再次弹跳。

保留键盘打开状态、底部 dock 隐藏和浅色根背景兜底，避免短表单露出黑色宿主底色。

补充小程序 web-view 原生 page 浅色背景和对应样式测试。

更新统一创作页与平台键盘适配文档，沉淀不再全局上移平台壳的约束。

miniprogram/pages/web-view/index.style.test.js

@@ -0,0 +1,32 @@
+import fs from 'node:fs';
+import path from 'node:path';
+
+import { describe, expect, test } from 'vitest';
+
+const PAGE_DIR = path.resolve(
+  process.cwd(),
+  'miniprogram/pages/web-view',
+);
+
+function readPageFile(fileName) {
+  return fs.readFileSync(path.join(PAGE_DIR, fileName), 'utf8');
+}
+
+describe('mini program web-view page background', () => {
+  test('keeps the native web-view host light when the mobile keyboard exposes it', () => {
+    const wxml = readPageFile('index.wxml');
+    const wxss = readPageFile('index.wxss');
+
+    expect(wxml).toContain('class="web-view-host"');
+    expect(wxml).not.toContain('class="web-view-page"');
+    expect(wxss).toContain('page');
+    expect(wxss).toContain('.web-view-host');
+    expect(wxss).toContain('background: #fffdf9;');
+
+    const webViewHostBlock = wxss.slice(
+      wxss.indexOf('.web-view-host'),
+      wxss.indexOf('.setup-screen'),
+    );
+    expect(webViewHostBlock).not.toContain('#0b0f14');
+  });
+});