fix(lanes): cloning into a deleted workspace's folder re-attaches it instead of failing UNIQUE

A workspace record outlives its folder (deleted from the File Explorer or a
shell). Cloning the same repo into that path again ran `git clone`, then
createLane hit idx_lanes_cwd_tool and answered 500 "UNIQUE constraint failed:
lanes.cwd, lanes.tool", leaving the new clone with no workspace on it.

POST /api/lanes/clone now looks for the caller's own workspace at exactly
that folder and tool and answers 200 { lane, created: false, path }, like
POST /ensure. Another user's workspace there is still refused before the
clone (folderTakenByOther), and a nested path still makes its own workspace.

server/__tests__/git-clone.test.js

@@ -143,6 +143,25 @@ describe("POST /api/lanes/clone", () => {
     assert.equal(again.body.error.code, "EEXISTS");
   });
 
+  it("re-attaches a workspace whose folder was deleted instead of failing UNIQUE", async () => {
+    const first = await request("POST", "/api/lanes/clone", {
+      url: "https://forge.test/o/r.git",
+      parent: WORK,
+      name: "gone",
+    });
+    assert.equal(first.status, 201, JSON.stringify(first.body));
+    fs.rmSync(path.join(WORK, "gone"), { recursive: true, force: true });
+    const again = await request("POST", "/api/lanes/clone", {
+      url: "https://forge.test/o/r.git",
+      parent: WORK,
+      name: "gone",
+    });
+    assert.equal(again.status, 200, JSON.stringify(again.body));
+    assert.equal(again.body.created, false);
+    assert.equal(again.body.lane.id, first.body.lane.id);
+    assert.ok(fs.existsSync(path.join(WORK, "gone", "README.md")));
+  });
+
   it("clones over ssh with the user's key, kept in the clone's config", async () => {
     const made = await request("POST", "/api/me/git/ssh-key", {});
     assert.equal(made.status, 201);