feat: display campaign createdAt in UI card

Campaign card now shows created date/time next to char/encounter counts.
Lets DM tell newest campaign apart (replay tool creates many).

createdAt already set at campaign create (line 2174). Display renders
formatted: 'Jul 1, 2026, 16:32'.

replay-combat.js: campaign + encounter names now include timestamp
(new Date().toLocaleString) for easy identification.

WS collection push verified live (injected test campaigns appeared
without reload).

src/App.js

@@ -2284,6 +2284,11 @@ function AdminView({ userId }) {
                         <span className="inline-flex items-center">
                           <Swords size={12} className="mr-1" /> {campaign.encounterCount === undefined ? '...' : campaign.encounterCount} Encounters
                         </span>
+                        {campaign.createdAt && (
+                          <span className="inline-flex items-center opacity-80">
+                            {new Date(campaign.createdAt).toLocaleDateString('en-US', { year: 'numeric', month: 'short', day: 'numeric', hour: '2-digit', minute: '2-digit', hour12: false })}
+                          </span>
+                        )}
                       </div>
                     </div>
                     <button