enable transfer of multiple files using wildcards

from everything i can tell, the `multipass transfer` command is only useful for transferring single files/folders from a multipass instance to the host. for example, the command `multipass transfer :dir/filename* .` will give an SFTP error and actually create a file called `*` on the host (which itself seems very dangerous because it may prompt one to to want to run `rm *` instead of `rm \*`).

there is nothing in the documentation that says that wildcards are not supported, but that seems to be the case. honestly, i'm surprised that this is not supported, so if it is not, i would expect the documentation to be fairly clear about it. i see that there is a `--recursive` option, but that copies the parent directory and all of its contents, unlike what a wildcard would do.

Start by tracing the `multipass transfer` command's handling of a source such as `instance:dir/filename*`, then compare it with the existing `--recursive` behavior. Confirm how wildcard sources should be interpreted and ensure the result transfers the matching files without creating a literal `*`; update documentation if wildcard support remains unavailable.

Written by the indexing model from the issue text.