Composer window should auto-hide more dynamically

Composer window should auto-hide after sending email. If it already auto-hides, then timeout should be shorter. Alternatively it should immediately auto-hide on sent, and a notification box displayed with result of sending.

Start by locating the Composer window's send flow and inspect how it currently handles auto-hiding after an email is sent. Determine whether the timeout or sent-state behavior is responsible, then confirm the chosen behavior with the sending result notification. Done means the Composer window hides as specified and the result remains visible to the user.

Written by the indexing model from the issue text.