Point Admin back button at the active game, not the join screen

The Admin page's back button now returns to this browser's own Pi-Rat
dashboard for the game (looked up from the saved sessions), labelled
"← Back to Game". Falls back to the join page only when this browser has
no saved session for the game.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

TODO.md

@@ -16,7 +16,7 @@
 
 - [x] Captain should not be autoassigned. That's something the crew has to earn.
 
-- [ ] The back button on the admin page should go back to the active game, not the join screen
+- [x] The back button on the admin page should go back to the active game, not the join screen
 
 - [ ] Add a toast pop-up for new events entering the event log, that then fades into the event log button
 

frontend/src/pages/Admin.svelte

@@ -2,11 +2,21 @@
     import { onMount } from 'svelte';
     import { apiRequest } from '../lib/api';
     import { setPageTitle } from '../lib/title';
+    import { getSessions } from '../lib/sessions';
 
     export let params = {};
     let gameId = params.id;
     let adminKey = '';
 
+    // Return to this browser's own Pi-Rat dashboard for the game (the most
+    // recently used session), not the public join screen. Falls back to join
+    // if this browser has no saved session for the game.
+    $: mySession = getSessions().find(s => s.gameId === gameId);
+    $: backLink = mySession
+        ? `/#/game/${gameId}/player/${mySession.playerId}`
+        : `/#/game/${gameId}/join`;
+    $: backLabel = mySession ? '← Back to Game' : 'Back to Game Join Page';
+
     let data = null;
     let error = '';
     let copiedPlayerId = null;
@@ -187,7 +197,7 @@
             </table>
 
             <div class="mt-8">
-                <a href="/#/game/{gameId}/join" class="btn btn-secondary">Back to Game Join Page</a>
+                <a href={backLink} class="btn btn-secondary">{backLabel}</a>
             </div>
         </div>
     {/if}