style(chat): consistent, visible message bubbles (user was an invisible outline)

Author: ishaan1124

frontend/ui/src/components/message-part.css

@@ -76,8 +76,8 @@
     white-space: pre-wrap;
     word-break: break-word;
     overflow: hidden;
-    background: var(--surface-weak);
-    border: 1px solid var(--border-weak-base);
+    background: var(--surface-raised-base);
+    border: 1px solid var(--border-base);
     padding: 10px 14px;
     border-radius: 14px;
 

frontend/ui/src/components/session-turn.css

@@ -222,7 +222,7 @@
     [data-slot="session-turn-response"] {
       position: relative;
       width: 100%;
-      border: 1px solid var(--border-weak-base);
+      border: 1px solid var(--border-base);
       border-radius: 14px;
       padding: 16px 18px;
       background: var(--surface-raised-base);