refactor(chat): migrate simple bubble styles to tailwind

src/app/chat/components/text-bubble.tsx

@@ -8,17 +8,27 @@
  *   - AI 消息：白底黑字 + 左上角尖角
  *   - 用户消息：渐变（primaryGradient）+ 白字 + 右上角尖角
  */
-import styles from "./text-bubble.module.css";
 
 export interface TextBubbleProps {
   content: string;
   isFromAI: boolean;
 }
 
+const BASE_CLASS_NAME =
+  "w-full self-stretch whitespace-pre-wrap break-words rounded-[var(--radius-xxl,24px)] px-[var(--spacing-4,16px)] py-[var(--spacing-3,12px)] text-[length:var(--chat-message-font-size,var(--responsive-body,16px))] leading-[var(--chat-message-line-height,1.5)] shadow-[var(--shadow-input-box,0_1px_2px_rgba(0,0,0,0.1))]";
+
+const AI_CLASS_NAME =
+  "rounded-tl-none bg-white text-[var(--color-text-foreground,#000)]";
+
+const USER_CLASS_NAME =
+  "rounded-tr-none bg-[linear-gradient(to_right,var(--color-button-gradient-start,#ff67e0),var(--color-button-gradient-end,#ff52a2))] text-white";
+
 export function TextBubble({ content, isFromAI }: TextBubbleProps) {
   return (
     <div
-      className={`${styles.bubble} ${isFromAI ? styles.bubbleAi : styles.bubbleUser}`}
+      className={[BASE_CLASS_NAME, isFromAI ? AI_CLASS_NAME : USER_CLASS_NAME]
+        .filter(Boolean)
+        .join(" ")}
     >
       {content}
     </div>