ext-v0.5.4

Automated extension build. NOT yet submitted to the Chrome Web Store — download the zip and upload it deliberately. See docs/extension-rollout.md.

What's Changed

• B82–B85: teammate matches, settings overhaul, account-centric, remove public replays by @pmossman in #2
• B86: enforce safe deploys (expand/contract migration guard) by @pmossman in #3
• B87: bump CI off Node 20 (GitHub Actions deprecation) by @pmossman in #4

Full Changelog: ext-v0.5.3...ext-v0.5.4