fix: version display and comparison issues

- Remove duplicate 'v' prefix in version display
- Add version string cleanup (trim spaces, remove v/V prefix)
- Use custom download URL when set
- Fix has_update logic for same version comparison

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/internal/router/app/info.go

@@ -1,6 +1,7 @@
 package app
 
 import (
+	"strings"
 	"verification-platform-backend/internal/database"
 	"verification-platform-backend/internal/model"
 	"verification-platform-backend/internal/service"
@@ -92,10 +93,19 @@ func handleAppCheckUpdate(c *gin.Context) {
 		return
 	}
 
+	// 清理版本号：去除空格和前缀 v/V
+	cleanVersion := func(v string) string {
+		v = strings.TrimSpace(v)
+		v = strings.TrimPrefix(v, "v")
+		v = strings.TrimPrefix(v, "V")
+		return v
+	}
+	clientVersionClean := cleanVersion(clientVersion)
+
 	// 找到客户端当前版本对应的版本记录
 	var clientVersionRecord *model.Version
 	for i := range allVersions {
-		if allVersions[i].Version == clientVersion {
+		if cleanVersion(allVersions[i].Version) == clientVersionClean {
 			clientVersionRecord = &allVersions[i]
 			break
 		}
@@ -171,12 +181,18 @@ func handleAppCheckUpdate(c *gin.Context) {
 		}
 	}
 
+	// 确定下载地址：优先使用自定义地址
+	downloadURL := latestVersion.FilePath
+	if latestVersion.CustomDownloadURL != "" {
+		downloadURL = latestVersion.CustomDownloadURL
+	}
+
 	// 构建返回结果
 	result := map[string]interface{}{
 		"has_update":      true,
 		"current_version": clientVersion,
 		"latest_version":  latestVersion.Version,
-		"download_url":    latestVersion.FilePath,
+		"download_url":    downloadURL,
 		"file_size":       latestVersion.FileSize,
 		"file_hash":       latestVersion.FileHash,
 		"entry_file":      latestVersion.EntryFile,