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/pages/Exchanges/ExchangesPage.module.css

@@ -1,10 +1,16 @@
-.threeColumn {
+.splitView {
   display: grid;
-  grid-template-columns: 280px 1fr;
+  grid-template-columns: 1fr 1fr;
   height: 100%;
   overflow: hidden;
 }
 
+.leftPanel {
+  overflow: auto;
+  height: 100%;
+  border-right: 1px solid var(--border);
+}
+
 .rightPanel {
   display: flex;
   flex-direction: column;