chore: cut 0.0.521

[DEENUU1]

Summary

Release 0.0.521: version, lock and changelog.

Changes

• backend/pyproject.toml, frontend/package.json and backend/uv.lock move to 0.0.521.
• CHANGELOG.md: the [Unreleased] block becomes [0.0.521] - 2026-10-06, with a fresh empty [Unreleased] above it.
• Ships fix(auth): answer a refresh burst with one successor token #2018 (from fix(auth): answer a refresh burst with one successor token #2007):
  • a burst of refreshes on one cookie is answered with the one successor token the session holds, so the cookie converges instead of being cleared;
  • a refused refresh logs the console out and sends the person to sign in.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-06T12:25:44.446972Z	2319789	PR opened
🔒 Security Review	✅ Completed 2026-10-06T12:26:30.800753Z	2319789	PR opened

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