fix(ui): restore layout — same table everywhere, 50:50 split, full-height sidebar, tab styling

- Sidebar wrapper gets height:100% to fill window
- Route-scoped Exchanges uses same Dashboard table (not compact ExchangeList)
- 50:50 grid split: table on left, diagram on right when route selected
- ContentTabs gets border-bottom and surface background for visibility

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/components/ContentTabs.module.css

@@ -1,5 +1,5 @@
 .wrapper {
-  padding: 0 1.5rem;
-  padding-top: 0.75rem;
-  padding-bottom: 0;
+  padding: 0.625rem 1.5rem 0;
+  border-bottom: 1px solid var(--border);
+  background: var(--surface);
 }