fix(chat): improve text bubble layout to fill width and prevent overflow

src/app/chat/components/message-content.tsx

@@ -29,9 +29,12 @@ export function MessageContent({ content, imageUrl, isFromAI }: MessageContentPr
       style={{
         display: "flex",
         flexDirection: "column",
+        // **关键**：在 row flex 父中撑开（不依赖 content 循环）—— 让 TextBubble 能拿到真实宽度
+        flex: "1 1 0",
+        // 防超长 content（图片 / 超长 url）撑爆父
+        minWidth: 0,
         alignItems: isFromAI ? "flex-start" : "flex-end",
         gap: 8,
-        maxWidth: "100%",
       }}
     >
       {hasImage && imageUrl && <ImageBubble imageUrl={imageUrl} />}