style(admin/workbench): 上方 5 个 KPI stat-card 改为深色底白字

改动 (仅 CSS, 业务逻辑 100% 保留):
- .stat-card 背景: #fff → linear-gradient var(--brand-primary) → var(--brand-primary-deep)
- .stat-card 边框: 1px solid #f0f0f0 → 删 (深色底不需要边框)
- .stat-card 文字: inherit → #fff (白字)
- .stat-card hover: border-color 变化 → translateY(-2px) + 蓝色阴影上浮
- .stat-label 颜色: #8c8c8c → rgba(255,255,255,0.75) (白字次级)
- .stat-value 渐变文字 hack → 直接 color: #fff (去掉 -webkit-background-clip/text-fill-color)

视觉效果: 5 个 KPI 卡变深海军蓝渐变方块, 白字 + 半透明 label, 鼠标 hover 上浮 2px

不变: 模板/grid 布局/点击跳转逻辑/data load 函数 都不动

ry-vue3/src/views/admin/Workbench.vue

@@ -99,30 +99,26 @@ onMounted(load)
 
 .stats-grid { display: grid; grid-template-columns: repeat(5, 1fr); gap: 16px; margin-bottom: 12px; }
 .stat-card {
-  background: #fff;
-  border: 1px solid #f0f0f0;
+  background: linear-gradient(135deg, var(--brand-primary) 0%, var(--brand-primary-deep) 100%);
   border-radius: 8px;
   padding: 24px;
   cursor: pointer;
   text-decoration: none;
-  color: inherit;
+  color: #fff;
   display: flex;
   flex-direction: column;
   align-items: center;
   justify-content: center;
-  transition: border-color 0.2s, box-shadow 0.2s;
+  transition: transform 0.2s, box-shadow 0.2s;
   min-height: 120px;
 }
-.stat-card:hover { border-color: var(--brand-primary); box-shadow: 0 2px 8px rgba(30,58,138,0.15); }
-.stat-label { font-size: 14px; color: #8c8c8c; margin-bottom: 16px; }
+.stat-card:hover { transform: translateY(-2px); box-shadow: 0 6px 16px rgba(21,42,102,0.4); }
+.stat-label { font-size: 14px; color: rgba(255,255,255,0.75); margin-bottom: 16px; }
 .stat-value {
   font-size: 32px;
   font-weight: 600;
   line-height: 1.2;
-  background: linear-gradient(135deg, var(--brand-primary) 0%, var(--brand-primary-deep) 100%);
-  -webkit-background-clip: text;
-  -webkit-text-fill-color: transparent;
-  background-clip: text;
+  color: #fff;
 }
 
 .hint-text { font-size: 12px; color: #8c8c8c; margin: 12px 0 20px; text-align: center; }