修复发出消息里的超链接因为和气泡背景同色而完全不可见的问题

上一版把发出气泡背景改成蓝色（--clr-primary-accent）时漏了一处：全局 a{color} 用的正是同一个
token，链接文字和气泡背景撞成一模一样的颜色，肉眼完全看不见（但DOM里其实是好的，实测<a href>
标签和完整URL文本都在）。用真实账号发一条带链接的消息复现后确认。改为链接色跟随气泡文字的白色+
下划线，颜色不能再区分链接和普通文字时用下划线区分。

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

css/base.css

@@ -4636,6 +4636,18 @@ video {
   background-color: var(--clr-bubble-right-bg-flash);
 }
 
+/* Same collision as the read-receipt checkmark below: the global `a` rule (css/base.css:1970)
+   colors links with --clr-primary-accent, which is now this bubble's own background -- an
+   auto-linked URL in a sent message rendered with 0 contrast, invisible text that was still
+   very much there in the DOM (confirmed live: a real <a href> with the full URL as its text).
+   Underline is what marks it as a link now that color can't. */
+.right .bubble a,
+.right .bubble a:hover,
+.right .bubble a:focus {
+  color: var(--clr-bubble-right-text);
+  text-decoration: underline;
+}
+
 .right .bubble.tip {
   border-bottom-right-radius: 0;
 }