feat: clean up distrobox exports/entries even if container is already deleted

[iTrooz]

See #2059

[iTrooz]

I also added a failsafe on cleanup() because I accidentally triggered it with an empty container name during tests, and ended up deleting a lot of other files on my computer. Tell me if you'd prefer me to remove it :)

[Copilot]

Pull request overview

Adds behavior to distrobox rm to also clean up exported binaries/desktop entries for explicitly requested containers even when the container no longer exists, aligning with the “Remove exported apps” workflow discussed in #2059.

Changes:

• Track explicitly requested container names that were not found/removed and run cleanup for them.
• Add a small slice helper to remove handled names from the explicit list.
• Add a guard in cleanup() for empty container names.

Comments suppressed due to low confidence (1)

pkg/commands/rm.go:88

• This fmt.Printf call lacks a trailing newline, which can make output from multiple deletions run together and be harder to read. Consider adding "\n" (and/or routing through the logger once available).

			//nolint:forbidigo // waiting for the logger implementation
			fmt.Printf("error deleting %s: %s", currentDistrobox.Name, err)
		}

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[Copilot]

New behavior to run cleanup for explicitly requested but non-existent containers isn’t covered by tests. Consider adding a unit test to ensure it deletes only the expected exported artifacts and does not act on unsafe container names (e.g., empty, path traversal, glob chars).