Extend SetlistMCP to cover the full setlist.fm REST API

[adrianparker]

Summary

• Adds 11 new MCP tools covering every setlist.fm REST endpoint beyond the existing find_setlists/get_setlist pair: get_artist, find_artists, get_artist_setlists, get_venue, find_venues, get_venue_setlists, get_city, find_cities, list_countries, get_setlist_version, and get_user_setlists (attended/edited).
• Every new client method reuses the existing shared RateLimiter and TtlCache instances in server.js, so throttling and caching are inherited automatically with no new wiring.
• Collection endpoints treat a 404 from setlist.fm as an empty result (matching the existing search/setlists behavior); single-resource detail endpoints propagate 404 as a real not-found.
• list_countries walks setlist.fm's paginated country list internally and caches the merged result for a week — verified live that the API actually returns all 250 countries on page one, so this costs exactly one request in practice.
• Wires up the previously dead HTTP_MAX_ATTEMPTS env var through both API clients, since retry count directly affects request volume against a rate-limited API.
• Updates README.md and .env.example accordingly.

Test plan

• npm run lint — clean
• npm test — 285 passing (new client-method and tool tests added, test/server.test.js updated for the full tool list)
• npm run coverage — ~99% statements
• Manually smoke-tested every new client method against the live setlist.fm API (artists, venues, cities, countries, user setlists) to confirm response shapes and rate-limit behavior

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