fix: preserve IME composition in Enter handlers

[hugosmoreira]

Summary

• pass keyboard events to every non-chat Enter submission handler
• ignore Enter while an IME composition is active, including the keyCode === 229 fallback used by the existing chat input
• add a shared utility and regression coverage for composition and regular Enter events

Why

The main chat already protects CJK IME composition, but dialog and human-in-the-loop inputs still submitted when Enter was used to confirm a conversion candidate. This could send incomplete Japanese, Chinese, or Korean text.

Root cause

The affected Angular templates invoked their submit handlers without $event, so the handlers could not inspect isComposing.

Testing

• npm test -- --watch=false --browsers=ChromeHeadlessCI — 585 tests passed
• focused utility and dialog regression tests — 11 tests passed
• npm run build — passed

Fixes #469