fix: remove Party host allowlist

[amitbreuer]

Summary

• Remove Brewtify’s Party host allowlist check and PARTY_HOST_ALLOWLIST prerequisite/environment setting.
• Update host UI, error messages, documentation and tests to distinguish Spotify-owned app-access restrictions from a Brewtify allowlist.
• Preserve Spotify profile identity, account locking/one active room, verified Telegram sessions, isolated encrypted credentials, playback permissions, Premium confirmation and rate controls.

Validation reported by implementation session

• All five workspace builds, 20 API tests, 19 native PostgreSQL tests, 25 frontend tests and focused lint pass.
• A previously unlisted Spotify account completes OAuth and creates a room with no host-list configuration. Missing playback scopes and refresh credentials remain rejected.
• Actual browser verification is blocked by Chrome launch timeout and Chromium SIGSEGV before page loading. HTTP preview responds; this is not browser-rendering proof.

Preview

http://127.0.0.1:5217/app/?section=party&demo=host

Boundaries

No production/cloud changes, deployment, feature enablement or merge performed. Party remains disabled. Removing Brewtify’s allowlist does not bypass Spotify Development Mode access restrictions.