The clone-file-media-object RPC command only checked edit permissions
on the destination file. The source media object was fetched directly
by UUID without verifying the caller had access to the file that owns
it.
This fix adds a read permission check on the source file before
cloning. If the caller lacks read access to the source file, the
operation fails with :not-found to avoid leaking information about
the existence of files/media the caller cannot access.
Closes#11087
AI-assisted-by: qwen3.7-plus
cff9939552