perf(export): prioritize totals and keep table visible

src/pages/ExportPage.scss

@@ -439,6 +439,7 @@
   border-radius: 12px;
   background: var(--card-bg);
   padding: 12px;
+  flex: 1;
   min-height: 0;
   display: flex;
   flex-direction: column;
@@ -552,7 +553,8 @@
   overflow: hidden;
   border: 1px solid var(--border-color);
   border-radius: 10px;
-  min-height: 0;
+  min-height: 320px;
+  height: 100%;
   flex: 1;
 }