Library watcher reopens a library closed right after creation #3158

Issue description

Follow-up to #3145. LibraryManager's directory watcher debounces a new .sdlibrary folder for 500 ms and skips it only while the path is in creating. CreationGuard::drop removes the path as soon as creation finishes, while the folder's own create event is still pending. If the creator calls close_library inside the debounce window, the watcher opens the library again; the reopened copy holds .sdlibrary.lock and the next open fails with AlreadyInUse.

Since migrations run in one transaction (#3147), creation is fast enough to hit this window in normal runs. #3145 fixed the shutdown variant; this is the explicit-close variant.

Steps to reproduce

1. Create a library through LibraryManager.
2. Close it immediately.
3. Wait past the 500 ms debounce.
4. The library is open again, and reopening it fails with AlreadyInUse.

Platform and versions

• OS: Arch Linux (kernel 7.2)
• Spacedrive: main at 4d41a379f, built from source

bun 1.4.3
cargo 1.97.1 (c980f4866 2026-06-30)
rustc 1.97.1 (8bab26f4f 2026-07-14)

Check for other issues

• I've checked for other issues, and none exist.

Code of Conduct

• I agree to follow the Code of Conduct.