refactor(会员商品): 删除已无构造点的时长错误变体

- 移除 RuntimeProfileFieldError::InvalidRechargeProductDuration 及其 Display 分支；会员商品改走 InvalidRechargeProductKind 后该变体已无构造点。

server-rs/crates/module-runtime/src/errors.rs

@@ -88,7 +88,6 @@ pub enum RuntimeProfileFieldError {
     MissingProductTitle,
     InvalidRechargeProductPrice,
     InvalidRechargeProductPoints,
-    InvalidRechargeProductDuration,
     InvalidRechargeProductKind,
     InvalidRechargeProductFields,
     InvalidMembershipPlan,
@@ -183,9 +182,6 @@ impl std::fmt::Display for RuntimeProfileFieldError {
             Self::MissingProductTitle => f.write_str("recharge.product_title 不能为空"),
             Self::InvalidRechargeProductPrice => f.write_str("recharge.price_cents 必须大于 0"),
             Self::InvalidRechargeProductPoints => f.write_str("泥点商品 points_amount 必须大于 0"),
-            Self::InvalidRechargeProductDuration => {
-                f.write_str("会员商品 duration_days 必须大于 0")
-            }
             Self::InvalidRechargeProductKind => {
                 f.write_str("充值商品类型无效：会员商品已迁移到会员档位目录")
             }