fix(node): say so when MusicBrainz lookups are inert

Staying inert without a contact is the documented policy (module docstring,
musicbay.md §3.1): the usage policy wants a contact in the User-Agent, so an
unidentified client is never sent. Staying *silent* about it was not a
decision — the operator sees Music tiles with no metadata or cover art and
has nothing to search the logs for.

Warns once per client rather than once per lookup, since the condition is
constant for the client's lifetime.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DtfG7z6wHWj8RKHCvxQtY1

0 files changed, 0 insertions, 0 deletions