feat: click-outside dismiss and clean overlay styling

- Add invisible backdrop (z-index 99) behind expanded overlay to
  dismiss on outside click
- Remove background/padding from overlay wrapper so GroupCard
  renders without visible extra border
- Use drop-shadow filter instead of box-shadow for natural card
  shadow

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

ui/src/pages/AgentHealth/AgentHealth.tsx

@@ -722,6 +722,8 @@ export default function AgentHealth() {
                 onNavigate={() => navigate(`/runtime/${group.appId}`)}
               />
               {expandedApps.has(group.appId) && (
+                <>
+                <div className={styles.overlayBackdrop} onClick={() => animateToggle(group.appId)} />
                 <div
                   ref={(el) => {
                     if (!el) return;
@@ -758,7 +760,7 @@ export default function AgentHealth() {
                         />
                         <button
                           className={styles.collapseBtn}
-                          onClick={() => animateToggle(group.appId)}
+                          onClick={(e) => { e.stopPropagation(); animateToggle(group.appId); }}
                           title="Collapse"
                         >
                           <ChevronDown size={14} />
@@ -805,6 +807,7 @@ export default function AgentHealth() {
                     />
                   </GroupCard>
                 </div>
+                </>
               )}
             </div>
           ))}