fix: trade-pro workspace card description and preview colors (review round)

- design() desc map gains trade-pro entry (was rendering literal 'undefined')
- workspace.css: .theme-preview.trade-pro / .site-icon.trade-pro brand colors

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

app/static/workspace.css

@@ -2,3 +2,4 @@
 
 /* V8.12: task progress and dangerous actions, consistent focus and mobile sizing */
 .btn-danger{border:1px solid #f1c3c7;color:#a92840;background:#fff5f6}.btn-danger:hover{background:#feecee}.btn:disabled{opacity:.55;cursor:not-allowed}.build-row{min-width:0}.build-meta{overflow-wrap:anywhere}.site-card:focus-visible,.quick-card:focus-visible{outline:3px solid #80aaf6;outline-offset:2px}@media(max-width:570px){.build-row{align-items:flex-start;flex-wrap:wrap}.build-row>.inline-actions{width:100%;padding-left:0}.site-picker-wrap select{max-width:130px}}
+.theme-preview.trade-pro{background:linear-gradient(125deg,#0b3d91,#3d6dc1);color:#e8f1fb}.site-icon.trade-pro{background:#e8f1fb;color:#0b3d91}