smove does not support sequence-to-sequence rename syntax

[rsgalloway]

Summary

smove currently behaves more like "move sequence into directory" than a sequence-aware mv, which is surprising from the name and CLI shape.

For example, this intuitive rename attempt fails:

smove file01_%04d.rgb file03_%04d.rgb

with

Error: destination file03_%04d.rgb is not a directory

Problems
The second positional argument is always interpreted as a directory.

smove src_seq dest_seq does not work as a sequence rename.
Users have to write smove src_seq . --rename new_head instead.
--rename only accepts the basename prefix, not a full destination sequence pattern.

For file01_%04d.rgb, the required rename value is file03_, not file03_%04d.rg.
That is not very discoverable.
The CLI requires dest to already be an existing directory, but the implementation later calls os.makedirs(dest_dir, exist_ok=True).

So the CLI rejects destinations the move logic itself is prepared to create.

Expected Behavior
One of these should be supported clearly:

`smove src_seq dest_seq should perform an in-place sequence rename when dest is not a directory.
Or, if directory-only behavior is intentional, the CLI/help/docs should make that explicit and the error/help text should point users to --rename.