fix(vcs): Route a nested repository's own entry to the enclosing one and harden multi-root

Review fixes for several repositories in one project:

- A path equal to a nested repository's root (a submodule's entry, an untracked
  clone) belongs to the enclosing repository, in the backend and the Commit view.
  It was routed to the nested repository as ".", so Rollback ran `git restore` and
  `git clean` over the whole submodule and Commit staged everything in it.
- Repository-scoped commands take the repository root exactly and fail when it is
  gone instead of running in an enclosing repository; path-based ones resolve the
  file's repository (Project::with_repo_of).
- The rescan on a repository appearing or going watches `.git/HEAD`: the watcher
  never reports a `.git` path itself, so the old check never fired.
- Status skips a repository that cannot be read; refresh falls back to the primary
  repository when the selected one is gone instead of failing every time.
- Commit and Compare-with-Local diffs resolve repository-relative paths against the
  selected repository's root, not the project root.
- Update Project and Fetch go on after a failing repository and report the failures
  together; Update skips repositories with a detached HEAD or no upstream.
- The Push dialog leaves out a repository that cannot be read.
- Shelve and patches fail clearly for changes of a nested repository instead of
  leaving them out silently (they still support the main repository only).
- Fix the repository discovery test on Windows (path separators); Chinese text for
  the new strings.

src/features/vcs/diffInput.ts

@@ -4,7 +4,8 @@ import { call, commands } from "@/platform/ipc";
 import { editorService, type EditorInput } from "@/workbench/contributions";
 import { baseName, effectiveKind } from "./model";
 import { readWorkingText } from "./ops";
-import { statusOf, useVcs } from "./store";
+import { renamedFromPath } from "./changes";
+import { currentRepoRoot, statusOf } from "./store";
 
 export type DiffSide =
   /** File content at a git revision (`HEAD`, `:0` = index, a commit id, `<id>^`). */
@@ -104,15 +105,16 @@ export function workingDiffData(path: string, line?: number): DiffData {
     kind === "untracked" || kind === "added"
       ? { type: "text", text: "", label: "(does not exist)" }
       : st?.renamedFrom
-        ? { type: "rev", rev: "HEAD", path: joinRoot(st.renamedFrom), label: `HEAD (${st.renamedFrom})` }
+        ? { type: "rev", rev: "HEAD", path: renamedFromPath(st) ?? undefined, label: `HEAD (${st.renamedFrom})` }
         : { type: "rev", rev: "HEAD" };
   const right: DiffSide =
     kind === "deleted" ? { type: "text", text: "", label: "(deleted)" } : { type: "worktree" };
   return { path, left, right, line };
 }
 
+/** A path of the selected repository's log (repository-relative) made absolute. */
 function joinRoot(rel: string): string {
-  const root = useVcs.getState().root;
+  const root = currentRepoRoot();
   return root ? `${root}/${rel}` : rel;
 }