refactor(mp): 统一空状态为 EmptyState 组件 + 清理旧 Tab CSS

- 4 个页面的内联空状态替换为共享 EmptyState 组件
  (messages / action-inbox / pkg-health/alerts / mall)
- 清理 10 个页面的旧 Tab CSS（迁移到 SegmentTabs 后不再需要）
- 清理 elder-mode 中已删除的 mall-empty-state 引用

apps/miniprogram/src/pages/mall/index.scss

@@ -207,58 +207,3 @@
   }
 }
 
-/* ─── 空状态 ─── */
-.mall-empty-state {
-  display: flex;
-  flex-direction: column;
-  align-items: center;
-  justify-content: center;
-  padding: 100px 40px;
-}
-
-.empty-icon {
-  width: 120px;
-  height: 120px;
-  border-radius: 50%;
-  background: $pri-l;
-  @include flex-center;
-  margin-bottom: 32px;
-}
-
-.empty-char {
-  font-family: 'Georgia', 'Times New Roman', serif;
-  font-size: var(--tk-font-hero);
-  font-weight: bold;
-  color: $pri;
-  line-height: 1;
-}
-
-.empty-title {
-  font-size: var(--tk-font-body-lg);
-  font-weight: 600;
-  color: $tx;
-  margin-bottom: 12px;
-}
-
-.empty-hint {
-  font-size: var(--tk-font-h1);
-  color: var(--tk-text-secondary);
-  text-align: center;
-  margin-bottom: 24px;
-}
-
-.empty-action {
-  background: $pri;
-  border-radius: $r;
-  padding: 16px 48px;
-
-  &:active {
-    opacity: 0.85;
-  }
-}
-
-.empty-action-text {
-  font-size: var(--tk-font-body-lg);
-  color: $white;
-  font-weight: 600;
-}