Add player kicking for admins

Admins can now kick players from the Admin panel so a vanished player can't
stall the table. crud.kick_player removes a player mid-game: it drops their
captaincy, deletes their votes and any Challenge they're part of, and repairs
every other player's pointers to them (pending swap offers are cleared;
delegated Like/Hate questions and recruit technique slots are handed to a
present crewmate, or pool-filled when no one is left). The row is then deleted
— a kicked player's hand simply stops being "in play", so it returns to the
discard automatically. Finally recheck_phase_completion advances the phase if
the kicked player was the last thing it was waiting on.

Auth mirrors set-admin (admin-key on POST /api/game/{gid}/admin/kick). The one
guard is that the last remaining Admin can't be kicked, so the table is never
locked out of its own panel; a vanished creator can still be kicked once a
co-admin exists. The Admin panel gains a per-row Kick button (with a confirm),
shown as "—" for the last admin.

To support re-checking phase completion after a kick, each phase's
"everyone's done -> advance" gate was extracted into an idempotent maybe_*
helper, and recheck_phase_completion dispatches the right one per Game.phase.

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

frontend/src/pages/Admin.svelte

@@ -69,6 +69,26 @@
             error = err.message;
         }
     }
+
+    // The last remaining Admin can't be kicked, so the table is never locked out.
+    $: adminCount = data ? data.players.filter((p) => p.is_admin).length : 0;
+    function canKick(p) {
+        return !(p.is_admin && adminCount <= 1);
+    }
+
+    async function kickPlayer(p) {
+        const who = p.player_name || p.name;
+        if (!confirm(`Kick ${who} from the game? Their cards go to the discard and they'll have to rejoin. This can't be undone.`)) return;
+        try {
+            await apiRequest(`/game/${gameId}/admin/kick`, 'POST', {
+                key: adminKey,
+                target_player_id: p.id,
+            });
+            await loadAdminData();
+        } catch (err) {
+            error = err.message;
+        }
+    }
 </script>
 
 <div class="admin-page">
@@ -91,6 +111,10 @@
             <p><strong>Phase:</strong> {data.game.phase}</p>
             <p><strong>Admin Key:</strong> <span class="admin-key-chip">{data.game.admin_key}</span></p>
 
+            {#if error}
+                <div class="alert alert-danger mt-4">{error}</div>
+            {/if}
+
             <h3 class="mt-8 mb-4">Invite Link</h3>
             <p class="info-text">Share this link to let new players join the crew.</p>
             <div class="link-copy-action">
@@ -112,6 +136,7 @@
                         <th>Rank</th>
                         <th>Admin</th>
                         <th>Re-join Link</th>
+                        <th>Kick</th>
                     </tr>
                 </thead>
                 <tbody>
@@ -149,6 +174,13 @@
                                     </button>
                                 </div>
                             </td>
+                            <td>
+                                {#if canKick(p)}
+                                    <button on:click={() => kickPlayer(p)} class="btn btn-danger btn-small">Kick</button>
+                                {:else}
+                                    <span class="text-muted">—</span>
+                                {/if}
+                            </td>
                         </tr>
                     {/each}
                 </tbody>