Cin's review note: typing artist_name as plain `str` forced callers
that didn't have a name to pass `""` as a placeholder, which leaks the
parameter's emptiness contract into every call site and reads badly in
tests. Switching to `Optional[str] = None` lets callers omit it.
The function body's `if artist_name and active_server:` check already
handles None and "" identically, so no body changes were needed. Tests
that previously passed `artist_name=""` drop the argument; one new test
covers the omitted-arg path explicitly.
The web_server.py wrapper takes the same default for symmetry.
Broque Thomas