## Summary
- Each email row in the **Undo Log Detail** "Emails" section is now tappable.
- Tapping resolves the email via `EmailRepository.findEmailByMessageId(accountId, messageId)` and navigates to its **current** location, so the link survives the move/snooze that changed its IMAP UID.
- If the email has no Message-ID, or no row matches the lookup (e.g. hard-deleted), a SnackBar explains the situation instead of navigating.
A `chevron_right` trailing icon was added to signal the rows are now navigable.
Closes#474
## Test plan
- [x] New widget test `test/widget/undo_log_detail_screen_test.dart` covers:
- tap on a row whose lookup hits → navigates to `/accounts/<acc>/mailboxes/<encoded>/emails/<encoded>` with the **current** mailbox/id
- tap when lookup returns `null` → "Email no longer exists" SnackBar, no navigation
- tap when the original row has no Message-ID → "no Message-ID" SnackBar, no navigation
Co-authored-by: guettli <guettli@noreply.codeberg.org>
Reviewed-on: https://codeberg.org/guettli/sharedinbox/pulls/547
