IME composition triggers unexpected form submission and prevents newline input

When using an Input Method Editor (IME) such as Japanese, Chinese, or Korean, pressing Enter to confirm text composition triggers form submission instead of confirming the composition or inserting a newline.

Actual behavior:

Enter is treated as a submit action even during composition. On mobile devices, the Enter key is often replaced by a submit action, making it impossible to insert newlines at all.

This can be addressed by respecting composition events (compositionstart / compositionend) and avoiding Enter-to-submit behavior inside multiline inputs.