Two fixes for the UndoLog:
1. Don't delete the original undo log entry when undo is performed.
The entry stays in the log alongside the new inverse action, so
the user can retry the undo if it was silently reverted by an
IMAP sync.
2. Fix IMAP UID mismatch: after an IMAP move is applied on the server
the email gets a new UID in the destination folder. The undo service
now looks up the email by its RFC 2822 Message-ID when the original
row is gone, so the reverse-move pending change carries the correct
UID and actually succeeds on the server.
Add findEmailByMessageId to EmailRepository interface and impl.
Add a regression test that simulates the UID change scenario.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
