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.module.css

@@ -101,6 +101,15 @@
   background: var(--bg-hover);
 }
 
+.detailPanelOverride {
+  position: fixed;
+  top: 0;
+  right: 0;
+  height: 100vh;
+  z-index: 100;
+  box-shadow: -4px 0 24px rgba(0, 0, 0, 0.12);
+}
+
 .openDetailLink {
   display: inline-block;
   font-size: 13px;