setFlag/moveEmail/deleteEmail for IMAP accounts now enqueue to
pending_changes (with uid + mailboxPath in the payload) and apply an
optimistic local update, instead of calling the IMAP server directly.
flushPendingChanges dispatches on account type: JMAP uses the existing
Email/set path; IMAP opens one connection and drains all queued changes.
Connection failure marks every queued row with an incremented attempt
count so retries work correctly.
_AccountSync._sync() now calls flushPendingChanges before syncing so
queued mutations are delivered on the next poll.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
