feat(files): New → Clone repository clones into the open folder

The File Explorer's New menu (and its right-click menu) gains Clone
repository: it clones a URL into the folder it has open — of the user's own
home or of a workspace's own folder — through POST /api/lanes/clone with
that folder as `parent`, so the URL allowlist, the own-folder check and the
folder account's own git identity all apply, and opens a workspace on the
clone. ECREDENTIALS asks for a login, ESSHAUTH points to Settings → Git.
GET /api/homes now gives `me` its absolute `dir`. Keys typed in the dialog
never reach the explorer's shortcuts (Backspace / Delete).

server/__tests__/home-files.test.js

@@ -79,6 +79,8 @@ describe("File Explorer on the home", () => {
       r.body.homes.map((h) => [h.id, h.readOnly]),
       [["me", false]]
     );
+    // Its absolute folder: where the Files page's Clone repository clones to.
+    assert.equal(r.body.homes[0].dir, path.resolve(HOME));
   });
 
   it("lists the home with every top-level dot entry hidden", async () => {