fix(ui): unify HF file selection UI, remove cloud icon, add select-all, cleanup dead code (#965, #977)

- Unify single-URL and multi-URL HF repo flows to use the same batch
  preview interface (remove separate repoFileStep)
- Remove unnecessary cloud icon from HF batch preview items
- Use formatFileSize() instead of hardcoded MB text
- Change default selection to unchecked (no preselected files)
- Add select all / deselect all checkbox with dynamic Next button
- Clean up dead CSS, HTML template, and JS methods from removed
  repoFileStep
- Add selectAll i18n key with translations for all 10 locales
- Fix batch progress bar name fallback for HF items

locales/zh-TW.json

@@ -1136,6 +1136,7 @@
       "placeholder": "https://civitai.com/models/...",
       "urlHint": "每行輸入一個 CivitAI、CivArchive 或 Hugging Face URL。支援批量下載多個 URL。",
       "selectHfFiles": "選擇從此倉庫下載的檔案：",
+      "selectAll": "全選",
       "fetchingRepoFiles": "正在獲取倉庫檔案...",
       "locationPreview": "下載位置預覽",
       "useDefaultPath": "使用預設路徑",