Fix QQ IMAP history sync and add account controls

[bigfish1913]

Summary

• avoid QQ Mail BODYSTRUCTURE parsing failures during header/history sync
• add per-account Sync action in account management
• add confirmed local account removal with credential and cache cleanup
• include the existing feat/files-webdav-jmap feature branch history

Validation

• cargo fmt --all -- --check
• cargo check --bin flectar-mail --locked
• verified QQ IMAP history fetch locally

[iamdarkle]

Thanks for contributing this. I've added a few follow up fixes on your branch to make MIME recovery more resilient, fully refresh the UI after account removal, and improve the compact layout and removal confirmation, appreciate your work on this!