refactor(purchase): use URL/searchParams only for purchase query merge

frontend/src/views/user/PurchaseSubscriptionView.vue

@@ -117,17 +117,7 @@ function buildPurchaseUrl(
     url.searchParams.set(PURCHASE_UI_MODE_QUERY_KEY, PURCHASE_UI_MODE_EMBEDDED)
     return url.toString()
   } catch {
-    const params: string[] = []
-    if (userId) {
-      params.push(`${PURCHASE_USER_ID_QUERY_KEY}=${encodeURIComponent(String(userId))}`)
-    }
-    if (authToken) {
-      params.push(`${PURCHASE_AUTH_TOKEN_QUERY_KEY}=${encodeURIComponent(authToken)}`)
-    }
-    params.push(`${PURCHASE_THEME_QUERY_KEY}=${encodeURIComponent(theme)}`)
-    params.push(`${PURCHASE_UI_MODE_QUERY_KEY}=${encodeURIComponent(PURCHASE_UI_MODE_EMBEDDED)}`)
-    const separator = baseUrl.includes('?') ? '&' : '?'
-    return `${baseUrl}${separator}${params.join('&')}`
+    return baseUrl
   }
 }