Bumps base version 2.8.1 → 2.8.2 and the docker-publish default tag. A stability + performance
release: Spotify reliability (Docker boot-hang #949, the token-cache re-auth fix, on-demand
Sync-to-Spotify), the "slow after update" password-manager fix + Max Performance mode (#948), and
large-library imports that no longer time out the import page (#947).
Updates the five release touch-points: web_server version, docker-publish default, pr_description.md,
helper.js WHATS_NEW + VERSION_MODAL_SECTIONS (current release + Earlier-in-2.8.1 summary), and the
new RELEASE_2.8.2_discord.md (truncated for Discord, 1351 chars).
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