use the ibus preedit

### Description

It's better to use the ibus preedit and submit the output when the user has finished typing a word.

Start by locating the Rust entry point that handles IBus input and examine how typed text is currently submitted. Research how IBus preedit and word completion are exposed, then implement the behavior described: keep the preedit visible while typing and submit the completed word. Done means the engine uses the preedit until the user finishes a word and then submits the output.

Written by the indexing model from the issue text.