Sync WorkspaceView queued bubble to indigo gradient (design language)

Matches the ChatView.vue update from the UI polish pass — queued bubbles
use linear-gradient(135deg, #6366f1, #4f46e5) and 18px border-radius
consistent with the Illuminated Transcript design language.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/views/WorkspaceView.vue

@@ -650,9 +650,9 @@ details[open] .thinking-summary::before {
 .queued-bubble {
   max-width: 80%;
   padding: 0.75rem 1rem;
-  border-radius: 16px;
+  border-radius: 18px;
   border-bottom-right-radius: 4px;
-  background: var(--color-primary);
+  background: linear-gradient(135deg, #6366f1, #4f46e5);
   color: #fff;
   opacity: 0.45;
   font-size: 0.95rem;