feat: 登录页背景色改为品牌暖橙

紫色渐变 #667eea→#764ba2 改为暖橙 #FFF7ED→#F97316，统一品牌视觉

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

cfc-frontend/pages/login/login.vue

@@ -262,7 +262,7 @@ export default {
 <style scoped>
 .login-container {
   min-height: 100vh;
-  background: linear-gradient(180deg, #667eea 0%, #764ba2 100%);
+  background: linear-gradient(160deg, #FFF7ED 0%, #F97316 100%);
   padding: 60rpx 40rpx;
 }