fix: improve chat input UX and IME composition handling

[JiahaoZhu11]

Summary

This PR improves the chat input component with two main enhancements:

1. Better UX for the input bubble - The entire input bubble now behaves as a cohesive input component
2. Fixed IME composition handling - Enter key now works correctly for Chinese/Japanese/Korean input

Changes

Chat Input UX

• Entire input bubble is now clickable to focus the textarea (not just the textarea itself)
• Added cursor-text cursor style to indicate the bubble is interactive
• Send button no longer shows tooltip or responds to hover when hidden (empty input)
• Removed focus outline from textarea since the outer bubble already shows focus state via focus-within

IME Composition Fix

• Added compositionstart/compositionend event handlers to track IME state
• Implemented skipNextEnter flag to differentiate between:
  • Enter to confirm character selection (should not send)
  • Enter to send message (should send)
• Fixes the issue where pressing Enter during IME composition would send the incomplete text instead of confirming the selected characters

Testing

• Click anywhere on input bubble → textarea focuses
• Empty input → send button hidden, no tooltip on hover
• With text → send button visible, tooltip shows on hover
• Type Chinese/Japanese/Korean with IME → Enter confirms selection
• After confirming IME selection → Enter sends message
• Click to select IME candidate → next Enter sends message correctly

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

[Golenspade]

can you deliver a snapshot,so we can align the visual design

[benjaminshafii]

Automated message: IME handling + click-to-focus UX looks good and matches the polished input behavior we want.

Two items:

• PR is currently CONFLICTING with dev; please rebase.
• Please double-check skipNextEnter doesn’t swallow a real Enter when there was no composition event (should be covered, but worth a quick test with IME + normal typing).

I can’t provide a snapshot from here; a short gif/screenshot of the updated input would help design review.