fix: DetailPanel slide-in now visible — fixed empty content bug and positioning

- Only render DetailPanel when detail data is loaded (key={selectedId} forces remount
  so internal activeTab state resets correctly)
- Override DetailPanel CSS with position:fixed to overlay on right side
  (AppShell layout doesn't support detail prop from child pages)

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

ui/src/pages/Dashboard/Dashboard.tsx

@@ -262,12 +262,16 @@ export default function Dashboard() {
         />
       </div>
 
-      <DetailPanel
-        open={!!selectedId}
-        onClose={() => setSelectedId(null)}
-        title={selectedId ? `Exchange ${selectedId.slice(0, 12)}...` : ''}
-        tabs={detailTabs}
-      />
+      {selectedId && detail && (
+        <DetailPanel
+          key={selectedId}
+          open={true}
+          onClose={() => setSelectedId(null)}
+          title={`Exchange ${selectedId.slice(0, 12)}...`}
+          tabs={detailTabs}
+          className={styles.detailPanelOverride}
+        />
+      )}
     </div>
   );
 }