fix(hub): use single position table header on desktop monitor cards

Render all exchange positions in one table row group instead of repeating column headers per symbol.

Co-authored-by: Cursor <cursoragent@cursor.com>

manual_trading_hub/static/app.css

@@ -1272,6 +1272,14 @@ body.market-chart-fs-open {
   margin-bottom: 0;
 }
 
+.pos-table-wrap {
+  margin-bottom: 8px;
+}
+
+.data-table-positions tbody tr:not(:last-child) td {
+  border-bottom: 1px dashed var(--border-soft);
+}
+
 .pos-action-group {
   display: inline-flex;
   flex-direction: row;