feat(ai-chat): 优化历史消息时间显示与搜索定位

- 时间显示人性化：昨天/前天/跨年日期
- 搜索上下导航修复 scroll-into-view 触发逻辑

lang/en-us/ai-chat/index.js

@@ -8,6 +8,11 @@ export const lang = {
 	send: 'Send',
 	retry: 'Retry',
 
+	// ====== Time Format ======
+	timeFormatToday: 'Today',
+	timeFormatYesterday: 'Yesterday',
+	timeFormatBeforeYesterday: 'Day before yesterday',
+
 	// ====== ai-chat-message ======
 	aiNickname: 'AI Assistant',
 	defaultNickname: 'Me',

lang/zh-cn/ai-chat/index.js

@@ -8,6 +8,11 @@ export const lang = {
 	send: '发送',
 	retry: '重试',
 
+	// ====== 时间格式化 ======
+	timeFormatToday: '今天',
+	timeFormatYesterday: '昨天',
+	timeFormatBeforeYesterday: '前天',
+
 	// ====== ai-chat-message ======
 	aiNickname: '智能助手',
 	defaultNickname: '我',