fix: show existing files when editing version

- Load files data when fetching version info
- Display uploaded file info with re-upload option
- Preserve original file data when canceling re-upload
- Add i18n for reupload button

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

frontend/src/plugins/i18n/en.json

@@ -1504,6 +1504,7 @@
         "customDownloadUrlPlaceholder": "e.g., https://your-cdn.com/download/app.zip",
         "previewCustomDownloadUrl": "Download URL",
         "useDefault": "Use Default",
+        "reupload": "Re-upload",
         "changelogPreview": "Changelog Preview",
         "noChangelog": "No changelog",
         "notUploaded": "Not uploaded",

frontend/src/plugins/i18n/zh.json

@@ -1482,6 +1482,7 @@
         "customDownloadUrlPlaceholder": "例如: https://your-cdn.com/download/app.zip",
         "previewCustomDownloadUrl": "下载地址",
         "useDefault": "使用默认地址",
+        "reupload": "重新上传",
         "changelogPreview": "更新日志预览",
         "noChangelog": "暂无更新日志",
         "notUploaded": "未上传",