Extend IMAPClientProtocol with storeFlags, moveMessage, copyMessage,
expunge, appendMessage, capabilities methods. Implement all six in
IMAPClient actor using NIOIMAPCore typed commands. Add multi-part
command support to IMAPConnection/IMAPCommandRunner for APPEND.
MockIMAPClient tracks all write calls for testing. SyncCoordinator
detects mailbox roles from LIST attributes with name-based fallback.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
