feat(ui): add draggable splitter between search results and diagram panel

ui/src/pages/Exchanges/ExchangesPage.module.css

@@ -1,6 +1,5 @@
 .splitView {
-  display: grid;
-  grid-template-columns: 1fr 1fr;
+  display: flex;
   height: 100%;
   overflow: hidden;
 }
@@ -8,14 +7,30 @@
 .leftPanel {
   overflow: auto;
   height: 100%;
-  border-right: 1px solid var(--border);
+  flex-shrink: 0;
+}
+
+.splitter {
+  width: 5px;
+  flex-shrink: 0;
+  cursor: col-resize;
+  background: var(--border);
+  transition: background 0.15s;
+  touch-action: none;
+}
+
+.splitter:hover,
+.splitter:active {
+  background: var(--amber);
 }
 
 .rightPanel {
+  flex: 1;
   display: flex;
   flex-direction: column;
   overflow: hidden;
   height: 100%;
+  min-width: 0;
 }
 
 .emptyRight {