Add player re-join links to admin page

Each player row now has Open/Copy actions for their dashboard link, so
the creator can recover access for players who lose their URL.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/pages/Admin.svelte

@@ -8,6 +8,19 @@
 
     let data = null;
     let error = '';
+    let copiedPlayerId = null;
+    let copiedTimer = null;
+
+    function rejoinLink(playerId) {
+        return `${window.location.origin}/#/game/${gameId}/player/${playerId}`;
+    }
+
+    function copyRejoinLink(playerId) {
+        navigator.clipboard.writeText(rejoinLink(playerId));
+        copiedPlayerId = playerId;
+        clearTimeout(copiedTimer);
+        copiedTimer = setTimeout(() => { copiedPlayerId = null; }, 2000);
+    }
 
     onMount(() => {
         // Try to load admin_key from local storage
@@ -58,6 +71,7 @@
                         <th class="p-3">Role</th>
                         <th class="p-3">Status</th>
                         <th class="p-3">Rank</th>
+                        <th class="p-3">Re-join Link</th>
                     </tr>
                 </thead>
                 <tbody>
@@ -78,6 +92,14 @@
                                 {/if}
                             </td>
                             <td class="p-3">{p.rank}</td>
+                            <td class="p-3">
+                                <div class="link-copy-action">
+                                    <a href={rejoinLink(p.id)} class="btn btn-secondary btn-small">Open</a>
+                                    <button on:click={() => copyRejoinLink(p.id)} class="btn btn-secondary btn-small">
+                                        {copiedPlayerId === p.id ? '✓ Copied' : 'Copy'}
+                                    </button>
+                                </div>
+                            </td>
                         </tr>
                     {/each}
                 </tbody>