feat(ui): right rail inventory placeholder and optional event log

- RightRail: add Inventory section (placeholder "Items coming soon") between
  Resources and Event Log, matching the existing heading style
- RightRail: gate Event Log section on prefs.showEventLog; add local-state
  collapse toggle with aria-expanded and chevron indicator
- SettingsPanel: add "Show event log" checkbox row bound to prefs.showEventLog
  via setPrefs, matching existing card styling
- PlayPanel: gate mobile EventLog behind prefs.showEventLog for consistency
  with desktop; mobile ResourceBar unchanged

src/ui/PlayPanel.tsx

@@ -5,6 +5,7 @@ import { EventLog } from './EventLog';
 import { ResourceBar } from './ResourceBar';
 
 export function PlayPanel() {
+  const showEventLog = useGameStore((s) => s.prefs.showEventLog);
   const columns = useGameStore((s) => s.actionColumns).filter(
     (col) => col.groups.length > 0 && col.groups.some((g) => g.actions.length > 0),
   );
@@ -55,9 +56,11 @@ export function PlayPanel() {
         </div>
       ) : null}
 
-      <div className="block md:hidden">
-        <EventLog />
-      </div>
+      {showEventLog && (
+        <div className="block md:hidden">
+          <EventLog />
+        </div>
+      )}
     </div>
   );
 }