feat: manually mirror opencoze's code from bytedance

Change-Id: I09a73aadda978ad9511264a756b2ce51f5761adf

frontend/packages/common/chat-area/plugin-chat-background/src/custom-components/chat-background-ui/index.module.less

@@ -0,0 +1,11 @@
+.mask {
+  pointer-events: none;
+
+  position: absolute;
+  z-index: 10;
+
+  width: 100%;
+  height: 216px;
+
+  background: linear-gradient(180deg, rgba(99, 99, 99, 40%) 0%, rgba(99, 99, 99, 0%) 100%);
+}

frontend/packages/common/chat-area/plugin-chat-background/src/custom-components/chat-background-ui/index.tsx

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2025 coze-dev Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+ 
+import { useShallow } from 'zustand/react/shallow';
+import { WithRuleImgBackground } from '@coze-common/chat-uikit';
+import {
+  type CustomComponent,
+  useReadonlyPlugin,
+  PluginName,
+} from '@coze-common/chat-area';
+
+import { type BackgroundPluginBizContext } from '../../types/biz-context';
+
+import styles from './index.module.less';
+
+export const ChatBackgroundUI: CustomComponent['MessageListFloatSlot'] = ({
+  headerNode,
+}) => {
+  const plugin = useReadonlyPlugin<BackgroundPluginBizContext>(
+    PluginName.ChatBackground,
+  );
+  const { useChatBackgroundContext } = plugin.pluginBizContext.storeSet;
+  const backgroundImageInfo = useChatBackgroundContext(
+    useShallow(state => state.backgroundImageInfo),
+  );
+  const isBackgroundMode =
+    !!backgroundImageInfo?.mobile_background_image?.origin_image_url;
+
+  return isBackgroundMode ? (
+    <>
+      {headerNode ? <div className={styles.mask}></div> : null}
+      <WithRuleImgBackground backgroundInfo={backgroundImageInfo} />
+    </>
+  ) : null;
+};