feat: fix mobile AI full-width layout and simplify instance stats

Move hub AI mobile CSS after desktop grid rules so chat fills the screen. Hide exchange and total-trade stat cards on phone across all instances and compact export bar.

Co-authored-by: Cursor <cursoragent@cursor.com>

static/instance_theme.css

@@ -1,3 +1,43 @@
+/* 实例页手机端：顶栏统计精简 */
+@media (max-width: 720px) {
+  .stat-box > .stat-item-desktop-only {
+    display: none !important;
+  }
+
+  .stat-box {
+    gap: 8px;
+    margin-bottom: 12px;
+  }
+
+  .stat-box > .stat-item:last-child:nth-child(odd) {
+    grid-column: 1 / -1;
+  }
+
+  .stat-item {
+    min-height: 64px;
+    padding: 10px 8px;
+  }
+
+  .stat-item .value {
+    font-size: 1.1rem;
+  }
+
+  .export-bar > span:first-child {
+    display: none;
+  }
+
+  .export-bar {
+    gap: 6px;
+    margin-bottom: 10px;
+  }
+
+  .export-bar a {
+    flex: 1 1 auto;
+    text-align: center;
+    min-width: 0;
+  }
+}
+
 /* 实例页亮色主题（覆盖模板内联暗色样式） */
 html[data-theme="light"] {
   color-scheme: light;