feat(vcs): compare folder selections with revisions across repositories (#602)

Compare with Branch or Revision only handled one file, so reviewing a folder meant opening each file. Folders, the project root and multiple selections now open a changes tree against the chosen revision, with per-file diffs on demand. A single file keeps its direct diff.

Each path resolves against its own repository through the root registry. In a multi-repo workspace the picker offers shared revisions such as "main in 3 repositories" as well as per-repository ones, results are grouped by repository, and content outside any repository or a repository missing the revision is stated in the result. Listing is cancellable and off the UI thread, includes worktree and untracked changes, and a rename leaving the selection shows as a delete. Show Diff on folders reuses the same tree.

Verified on macOS, and against a remote host over the server protocol. A remote window, Windows and Linux were not run.

Fixes #567

src/platform/locales/text/zh.json

@@ -5348,5 +5348,15 @@
   "No debug output available": "暂无可用的调试输出",
   "The attached process may not provide standard output to the debugger.": "附加的进程可能不会向调试器提供标准输出。",
   "Show in Debug Tool Window": "在调试工具窗口中显示",
-  "Suspended": "已暂停"
+  "Suspended": "已暂停",
+  "Cannot compare {root} against {label}: {error}": "无法将 {root} 与 {label} 比较：{error}",
+  "Compare with Branch or Revision": "与分支或修订比较",
+  "No changes against {revision} in 1 repository": "在 1 个仓库中与 {revision} 相比没有更改",
+  "No changes against {revision} in {repositories} repositories": "在 {repositories} 个仓库中与 {revision} 相比没有更改",
+  "Open or select a file or folder to compare": "打开或选择要比较的文件或文件夹",
+  "Selection is outside Git repositories": "所选内容不在 Git 仓库中",
+  "Skipped content outside Git repositories: {skippedLabel}": "已跳过 Git 仓库之外的内容：{skippedLabel}",
+  "in {length} repositories": "在 {length} 个仓库中",
+  "No repository in the selection has revision {label}": "所选内容中的仓库均无版本 {label}",
+  "{repoName} has no revision {label}": "{repoName} 没有版本 {label}"
 }