chore(master): release 2.81.2

[github-actions]

🤖 I have created a release beep boop

2.81.2 (2026-09-17)

Bug Fixes

• api: check isBounce for messages in the Inbox only (de05eff)
• api: decide isBounce at fetch time instead of storing a marker (2c81311)
• api: remove the bounces field and the store behind it (b67acb9)
• api: report isBounce and relatedMessageId in message responses (b551bfd)
• imap: run the shared arrival checks instead of IMAP wrappers (26cd53c)
• imap: share the bounce shape check with the API clients (a0302a2)
• imap: share the complaint shape check with the API clients (90a9825)
• imap: share the delivery-report shape check with the API clients (aa777df)

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