feat: 轮播标签功能 — 后台加标签字段 + 多色平行四边形

后台:
- 轮播表单新增: 标签(逗号分隔) / 跳转链接 / 按钮文字 / 按钮链接
- 标签字段提示: 云计算,高性价比,弹性伸缩

前台 CSS:
- 标签改为左对齐
- 6 种渐变色自动轮换: 蓝紫/粉红/绿/金/橙/紫
- 保持平行四边形 skewX + 发光效果

css/index.css

@@ -244,7 +244,7 @@
   display: flex;
   flex-wrap: wrap;
   gap: 10px;
-  justify-content: flex-end;
+  justify-content: flex-start;
 }
 
 .banner-tag-pill {
@@ -292,6 +292,37 @@
   opacity: 0.8;
 }
 
+/* 多色标签 — 每个标签自动分配不同渐变色 */
+.banner-tag-pill:nth-child(1) {
+  background: linear-gradient(135deg, #38BDF8 0%, #6366F1 100%);
+  box-shadow: 0 4px 12px rgba(56, 189, 248, 0.4);
+}
+
+.banner-tag-pill:nth-child(2) {
+  background: linear-gradient(135deg, #F472B6 0%, #EC4899 100%);
+  box-shadow: 0 4px 12px rgba(244, 114, 182, 0.4);
+}
+
+.banner-tag-pill:nth-child(3) {
+  background: linear-gradient(135deg, #34D399 0%, #059669 100%);
+  box-shadow: 0 4px 12px rgba(52, 211, 153, 0.4);
+}
+
+.banner-tag-pill:nth-child(4) {
+  background: linear-gradient(135deg, #FBBF24 0%, #F59E0B 100%);
+  box-shadow: 0 4px 12px rgba(251, 191, 36, 0.4);
+}
+
+.banner-tag-pill:nth-child(5) {
+  background: linear-gradient(135deg, #FB923C 0%, #EA580C 100%);
+  box-shadow: 0 4px 12px rgba(251, 146, 60, 0.4);
+}
+
+.banner-tag-pill:nth-child(n+6) {
+  background: linear-gradient(135deg, #A78BFA 0%, #7C3AED 100%);
+  box-shadow: 0 4px 12px rgba(167, 139, 250, 0.4);
+}
+
 /* 按钮优化 - 科技感渐变发光效果 */
 .banner-cont .btn2 {
   position: relative;