fix(admin-web): 修复通知页面 SCSS 变量名

使用正确的变量名:
- $bg-card -> $card-background
- $shadow-card -> $shadow-base
- $text-tertiary -> $text-disabled

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/admin-web/src/app/(dashboard)/notifications/notifications.module.scss

@@ -23,10 +23,10 @@
   }
 
   &__card {
-    background: $bg-card;
+    background: $card-background;
     border-radius: 12px;
     padding: 24px;
-    box-shadow: $shadow-card;
+    box-shadow: $shadow-base;
   }
 
   &__filters {
@@ -203,7 +203,7 @@
     display: flex;
     gap: 20px;
     font-size: 12px;
-    color: $text-tertiary;
+    color: $text-disabled;
   }
 
   // 表单样式
@@ -245,7 +245,7 @@
       }
 
       &::placeholder {
-        color: $text-tertiary;
+        color: $text-disabled;
       }
     }
 
@@ -257,7 +257,7 @@
 
   &__formHint {
     font-size: 12px;
-    color: $text-tertiary;
+    color: $text-disabled;
   }
 
   &__modalFooter {