fix(desktop): respect IME enter in edit composer

[2001Y]

What does this PR do?

Fixes the desktop app's inline user-message edit composer so Enter during IME composition confirms the candidate text instead of submitting the edited message.

The main message composer already tracks compositionstart/compositionend and ignores keydown while composing. This applies the same behavior to the current edit composer path (user-edit-composer.tsx), then flushes the finalized composition on composition end.

Guards:

• nativeEvent.isComposing
• local composition ref
• keyCode === 229 (legacy IME enter on some platforms)

Test plan

• Focused Vitest IME + sanitizer: 12/12
• Typecheck under Node 22
• Full Desktop Vitest: 1,696 passed, 1 skipped (prior full run) + eslint/build
• Rebased onto current main with range-diff equivalent patch

New head: 3374c099e0dab370f10ce9c421337343bfae1af1

[teknium1]

Thanks for the focused IME regression fix. The reported behavior still exists on current main: apps/desktop/src/components/assistant-ui/thread/user-edit-composer.tsx:573-576 submits unmodified Enter without checking composition state, and :475-476 synchronizes input during composition. The main composer already uses the proposed pattern at apps/desktop/src/app/chat/composer/index.tsx:303-312, :364-372, and :727-741.

Problems

• The PR targets the removed apps/desktop/src/components/assistant-ui/thread.tsx. Refactors 7ff6908a5 and fa7bce078 moved the implementation to thread/user-edit-composer.tsx, so this needs a mechanical port rather than a direct cherry-pick.
• Current main already has the test CSS.escape stub via 6016997a72bc34df899e2118fea958256d922cae; do not duplicate that part of the diff.

Suggested changes

• Port only the composition guard/flush and regression test to the current component and test paths.

Automated hermes-sweeper review.

[2001Y]

Follow-up update (author)

Rebased onto current main (f8b6d381e2f8e8b2cf84ac0e9e628ea062a173e3) and pushed after review/test pass.

What changed

• IME Enter guard moved to current component path: user-edit-composer.tsx.
• Guards on nativeEvent.isComposing, composition ref, and keyCode === 229.
• Regression tests in user-message-edit.test.tsx (no duplicate CSS.escape stub).

Verification

• Focused Vitest (IME + sanitizer): 12/12 passed
• Typecheck: pass (Node 22)
• Full Desktop Vitest previously: 1,696 passed, 1 skipped + eslint/build pass
• Range-diff equivalent across latest main rebases

New head: 3374c099e0dab370f10ce9c421337343bfae1af1.

[teknium1]

This fix landed on main via #86760, which consolidated the duplicate PRs for this bug (earliest submission by @satotakumi in #37487; all contributors credited in that PR's body). Closing as the fix is now merged. Thanks for catching it!