frontend: the per-agent UI typechecks under preact 11

preact 11's types reject the side panel's role=dialog on an aside, which the
nix agent-typecheck check runs. The drawer is a div, whose CSS is
class-based, so nothing else changes.

frontend/packages/agent/src/components/SidePanel.tsx

@@ -39,7 +39,7 @@ export function SidePanel({ open, title, onClose, children }: SidePanelProps) {
         onClick={onClose}
         aria-hidden="true"
       />
-      <aside
+      <div
         class={`agent-side-panel-drawer${open ? " open" : ""}`}
         role="dialog"
         aria-modal="true"
@@ -58,7 +58,7 @@ export function SidePanel({ open, title, onClose, children }: SidePanelProps) {
           </button>
         </div>
         <div class="agent-side-panel-body">{children}</div>
-      </aside>
+      </div>
     </>
   );
 }