feat: make award statistics panel collapsible

- Convert stats-section to collapsible details element
- Add expand/collapse indicator (▶/▼)
- Save screen space on mobile devices

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/client-screen/src/views/AdminControl.vue

@@ -819,11 +819,11 @@ onMounted(() => {
         </div>
       </section>
 
-      <!-- Section B.5: Award Statistics -->
+      <!-- Section B.5: Award Statistics (Collapsible) -->
-      <section class="control-section stats-section">
+      <details class="control-section stats-section collapsible-section">
-        <div class="section-header">
+        <summary class="section-header">
           <h2>📊 实时奖项统计</h2>
-        </div>
+        </summary>
         <div class="section-body">
           <div v-if="Object.keys(awardStats).length === 0" class="no-stats">
             暂无投票数据
@@ -845,7 +845,7 @@ onMounted(() => {
             </div>
           </div>
         </div>
-      </section>
+      </details>
 
       <!-- Section C: Global Controls -->
       <section class="control-section global-section">
@@ -1346,6 +1346,31 @@ $admin-danger: #ef4444;
   grid-column: span 2;
 }
 
+// Collapsible Section
+.collapsible-section {
+  &.control-section {
+    summary.section-header {
+      cursor: pointer;
+      list-style: none;
+      user-select: none;
+
+      &::-webkit-details-marker {
+        display: none;
+      }
+
+      h2::after {
+        content: ' ▶';
+        font-size: 0.7em;
+        opacity: 0.6;
+      }
+    }
+
+    &[open] summary.section-header h2::after {
+      content: ' ▼';
+    }
+  }
+}
+
 .no-stats {
   text-align: center;
   color: #666;