* Reject ambiguous library names and empty library-set entries
get_library_id() silently picked the first library matching a
requested name, so two libraries sharing a name would sync whichever
happened to come first in the server's response - not necessarily the
one the operator meant. It now raises ConfigError when a name matches
more than one library.
resolve_libraries() rejects an empty entry produced by an empty
LIBRARY_ID, 'a::b', or a leading/trailing ':' the same way, instead of
silently logging 'library not found' and moving on.
* Clarify get_library_id's ambiguity docstring and error message
Copilot review: the input can be a name or an ID, and the error said
'Library name' even for an ID collision; use neutral wording. Also
made the docstring's second sentence a complete one.
---------
Co-authored-by: Maxim Shulga <maxim.shulga@alludo.com>
