feat: 对齐 Waffo 包年/永久结账与客户端席位 API

同步 OpsXShell 档位定价与 Waffo 商品映射，补齐 checkout/webhook/设备列表契约，便于桌面端购买与满席释放。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/internal/service/payment/waffo_test.go

@@ -0,0 +1,64 @@
+package payment
+
+import (
+	"net/url"
+	"strings"
+	"testing"
+)
+
+func TestBuildCheckoutURL_YearlySubscription(t *testing.T) {
+	cfg := WaffoConfig{
+		StoreSlug:          "opsxshell-pwsi6m4n",
+		ProductIDYearly:    "PROD_2WmkUVoYWt0NN8OVEyC6n3",
+		ProductIDPerpetual: "PROD_0pcnzzT4nalEkkcdyIUoD5",
+		Currency:           "CNY",
+		Environment:        "test",
+		SuccessURL:         "opsxshell://pro/activated",
+	}
+	raw, err := BuildCheckoutURL(cfg, "ORD1", "dev-1", "a@b.c", "", "yearly")
+	if err != nil {
+		t.Fatal(err)
+	}
+	u, err := url.Parse(raw)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(u.Path, "PROD_2WmkUVoYWt0NN8OVEyC6n3") {
+		t.Fatalf("yearly product missing: %s", raw)
+	}
+	q := u.Query()
+	if q.Get("type") != "subscription" {
+		t.Fatalf("type=%s want subscription", q.Get("type"))
+	}
+	if q.Get("currency") != "CNY" {
+		t.Fatalf("currency=%s", q.Get("currency"))
+	}
+	if q.Get("test") != "true" {
+		t.Fatalf("test=%s", q.Get("test"))
+	}
+}
+
+func TestBuildCheckoutURL_PerpetualOnetime(t *testing.T) {
+	cfg := WaffoConfig{
+		StoreSlug:          "opsxshell-pwsi6m4n",
+		ProductIDYearly:    "PROD_2WmkUVoYWt0NN8OVEyC6n3",
+		ProductIDPerpetual: "PROD_0pcnzzT4nalEkkcdyIUoD5",
+		Currency:           "CNY",
+		Environment:        "test",
+		SuccessURL:         "opsxshell://pro/activated",
+	}
+	raw, err := BuildCheckoutURL(cfg, "ORD2", "dev-1", "a@b.c", "", "perpetual")
+	if err != nil {
+		t.Fatal(err)
+	}
+	u, err := url.Parse(raw)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(u.Path, "PROD_0pcnzzT4nalEkkcdyIUoD5") {
+		t.Fatalf("perpetual product missing: %s", raw)
+	}
+	if u.Query().Get("type") != "onetime" {
+		t.Fatalf("type=%s want onetime", u.Query().Get("type"))
+	}
+}