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.

docs/API.md

@@ -405,6 +405,7 @@ closing the dialog then only hides it behind a progress chip (click to reopen)
 ```
 POST /api/lanes/clone   Body: { url, parent, name?, title?, tool?, credentials?: { username, password, remember? }, partial?, progressToken? }
                         → 201 { lane, created: true, path }
+                        → 200 { lane, created: false, path }   (the user's own workspace already at that folder + tool, its folder deleted since)
 GET  /api/lanes/clone/progress/:token
                         → 200 { state: queued|running|done|failed, position, running, waiting, limit,
                                 phase: remote|receiving|resolving|checkout|other|null, label, percent, detail }