The Cloudflare proxy funnelled every user's MusicBrainz traffic onto a few
egress IPs, and MusicBrainz rate-limits 1 req/s per IP, so the budget was
shared across the whole userbase and produced 503s that worsen with growth.
MB read access needs no key and authentication does not raise the limit, so
the proxy added only the funnel; going per-IP makes the budget per-user.
- qbz-integrations MusicBrainzConfig default is now use_proxy=false (direct).
- client: handle HTTP 503 + Retry-After (not just 429, which the proxy used
to translate); add parse_retry_after; route search_recording_by_isrc and
search_artist through handle_response_status.
- src-tauri session_lifecycle: MusicBrainz V2 init/teardown pass use_proxy=false.
Slint inherits this via CoreBridge's default-constructed client.
cc