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/features/project-tree/contextMenu.test.ts

@@ -44,6 +44,7 @@ const OTHER_ACTIONS = [
   "vcs.addToVcs",
   "vcs.annotate",
   "vcs.showDiff",
+  "vcs.compareWithBranch",
   "vcs.rollback",
   "vcs.push",
 ];
@@ -129,6 +130,17 @@ describe("project view context menu", () => {
     }
   });
 
+  it("offers branch comparison for files, folders, their union and the project root", () => {
+    for (const nodes of [
+      [node("/p/a.py")],
+      [node("/p/src", true)],
+      [node("/p/src", true), node("/p/lib", true)],
+      [node("/p", true, true)],
+    ]) {
+      expect(sub(contextMenuItems(nodes), "Git")).toContain("Compare with Branch…");
+    }
+  });
+
   it("offers Show History for files, directories, multi-selection and the project root", () => {
     const dispose = registerActions([{ id: "vcs.showHistory", title: "Show History", run: () => undefined }]);
     try {