fix: prevent Enter from submitting during IME composition

[UnsongK]

Fix IME composition issue with Enter key.
When using CJK input methods(Chinese/Japanese/Korean), pressing Enter to confirm character selection was incorrectly triggering form submission.
This fix listens for compositionstart/compositionend events and blocks Enter keydown during active IME composition.

[lsdefine]

Thanks for the fix! Two changes needed:

1. Add OS guard: This IME issue only affects macOS — on Windows the browser correctly fires keydown after compositionend, so Enter never accidentally submits during composition. Please wrap the entire block with if os.name != 'nt': so Windows users don't get an unnecessary hidden iframe (which components.html(height=0) can still render as a visible empty element).

2. Compress the line count: Currently +32 lines for a non-core fix is too much — it shouldn't exceed the surrounding core logic in length. The JS and Python can be significantly condensed. Please tighten it up.

[lsdefine]

Thanks for the contribution! I've incorporated the IME fix into main with a few changes:

• Compressed the JS to a single line
• Added if os.name != 'nt': guard so Windows users are completely unaffected
• Removed the height parameter

Closing this PR. Appreciate the effort! 🙏