fix: 订阅模式登录验证、永久会员类型区分、动态代码HTTP返回值修复、侧边栏滚动位置保持

- 修复订阅模式登录时错误检查余额的问题
- 区分无限余额和永久订阅两种永久会员类型
- 修复动态代码HTTP请求返回值在JS中无法正确访问的问题
- 添加侧边栏滚动位置保持功能
- 移除developer角色相关代码，统一使用admin
- 添加缺失的i18n翻译key

backend/internal/router/app/account.go

@@ -116,13 +116,24 @@ func handleAppHeartbeat(c *gin.Context) {
 		}
 
 		if shouldDeduct {
-			if user.Balance >= app.DeductionAmount {
-				user.Balance -= app.DeductionAmount
-				log.Printf("[DEBUG] Deducted %.2f from user %d, new balance: %.2f", app.DeductionAmount, user.ID, user.Balance)
+			if user.Balance == -1 {
+				log.Printf("[DEBUG] User %d is permanent member, skip deduction", user.ID)
+			} else if app.BillingType == "subscription" {
+				if user.ExpiryAt == nil || user.ExpiryAt.Before(now) {
+					log.Printf("[DEBUG] User %d subscription expired, ExpiryAt=%v", user.ID, user.ExpiryAt)
+					response.Error(c, 403, "订阅已过期")
+					return
+				}
+				log.Printf("[DEBUG] User %d subscription valid, skip balance deduction", user.ID)
 			} else {
-				log.Printf("[DEBUG] User %d has insufficient balance: %.2f < %.2f", user.ID, user.Balance, app.DeductionAmount)
-				response.Error(c, 403, "余额不足")
-				return
+				if user.Balance >= app.DeductionAmount {
+					user.Balance -= app.DeductionAmount
+					log.Printf("[DEBUG] Deducted %.2f from user %d, new balance: %.2f", app.DeductionAmount, user.ID, user.Balance)
+				} else {
+					log.Printf("[DEBUG] User %d has insufficient balance: %.2f < %.2f", user.ID, user.Balance, app.DeductionAmount)
+					response.Error(c, 403, "余额不足")
+					return
+				}
 			}
 		}
 	}