Dismiss side panel when encounter becomes empty

Closes the stat block / source manager panel when the last combatant
is removed or the encounter is cleared, giving a fully clean state.

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

apps/web/src/App.tsx

@@ -30,6 +30,13 @@ export function App() {
 	const activeRowRef = useRef<HTMLDivElement>(null);
 	const actionBarAnim = useActionBarAnimation(encounter.combatants.length);
 
+	// Close the side panel when the encounter becomes empty
+	useEffect(() => {
+		if (isEmpty) {
+			sidePanel.dismissPanel();
+		}
+	}, [isEmpty, sidePanel.dismissPanel]);
+
 	// Auto-scroll to active combatant when turn changes
 	const activeIndex = encounter.activeIndex;
 	useEffect(() => {