fix: use self-portaling DetailPanel from design system v0.1.5

DetailPanel now portals itself to #cameleer-detail-panel-root (a div
AppShell places as a sibling of .main in the top-level flex row).
Pages just render <DetailPanel> inline — no manual createPortal,
no context, no prop drilling.

Remove the old #detail-panel-portal div from LayoutShell and the
createPortal wrappers from Dashboard and AgentHealth.

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

ui/src/components/LayoutShell.tsx

@@ -137,8 +137,6 @@ function LayoutContent() {
       <main style={{ flex: 1, overflow: 'auto', padding: '1.5rem' }}>
         <Outlet />
       </main>
-      {/* Portal target for DetailPanel — pages use createPortal to render here */}
-      <div id="detail-panel-portal" />
     </AppShell>
   );
 }