fix(cases): skip the cleanup when git never ran, and refuse Docker workspaces

A direct clone whose git-slot wait timed out came back with no spawnError, so
the cleanup emptied a folder git never touched. GitRun now says whether git
started and the cleanup requires it. Cloning into a folder at or inside a
Docker case workspace is refused, as git status, fetch and worktrees do, since
git would run the new repository's hooks and filters on the host.

docs/api-reference.md

@@ -1315,7 +1315,7 @@ The target is judged before anything is written:
 
 Admin only in multi-user mode (`403`), like `POST /api/cases/link`: it writes outside the cases directory and into the shared, ownerless registry. If anything fails after the first write, what this call created is removed (the whole folder if it created it, otherwise only the scaffold inside the empty folder you picked) and the response is `500`.
 
-`POST /api/cases/clone` takes the same optional `path`, with `{ name, repository, ref?, shallow?, description?, path? }`. Without `path` the repository is cloned to `<cases dir>/<name>` as always. With `path` the repository is cloned **into that exact folder** (no `<name>` subfolder is added) and registered as a linked case, judged by the same rules as above: `400` for an invalid or blocked path (or a symlink or file at the target), `404` for a missing parent, `422` for an unreachable parent, and `409 ALREADY_EXISTS` for a folder that has files, a name already in use or a folder that is already a case. Admin only in multi-user mode (`403`). An existing empty folder is cloned into directly and is kept, emptied again, if the clone fails; a second clone into the same folder while one is running is refused with `409`. If the clone succeeds but the registry write fails (or the name was linked while git ran, which is `409`), the cloned folder is kept and the error names it: `500 OPERATION_FAILED`, then use Link Existing.
+`POST /api/cases/clone` takes the same optional `path`, with `{ name, repository, ref?, shallow?, description?, path? }`. Without `path` the repository is cloned to `<cases dir>/<name>` as always. With `path` the repository is cloned **into that exact folder** (no `<name>` subfolder is added) and registered as a linked case, judged by the same rules as above: `400` for an invalid or blocked path (or a symlink or file at the target), `404` for a missing parent, `422` for an unreachable parent, and `409 ALREADY_EXISTS` for a folder that has files, a name already in use or a folder that is already a case. Admin only in multi-user mode (`403`). An existing empty folder is cloned into directly and is kept, emptied again, if the clone fails; a second clone into the same folder while one is running is refused with `409`. A destination at or inside a Docker case workspace is refused `400 INVALID_INPUT` (git would run the new repository's hooks and filters on the host, and a container can write there), and `503` when the Docker case list cannot be read. If the clone succeeds but the registry write fails (or the name was linked while git ran, which is `409`), the cloned folder is kept and the error names it: `500 OPERATION_FAILED`, then use Link Existing.
 
 ## Git status