feat(payment): 支付插件 - 合并 PR #546 易支付适配

Merge pull request #546 from qiuliw. Preserve the original author and current main behavior.

backend/internal/protocol/payment_artifact_test.go

@@ -17,6 +17,7 @@ var officialPaymentPackageIDs = []string{
 	"official-payment-alipay-page",
 	"official-payment-xunhupay",
 	"official-payment-zhifufm",
+	"official-payment-epay",
 }
 
 var officialPaymentTaggedArtifacts = []string{