fix(tui): clear input after Korean IME submit

[sweetcornna]

Summary

• distinguish a TextInput self-echo from an external controlled-value update
• allow the parent value="" update after submit to clear the internal buffer
• add a regression test for Korean IME text submitted immediately after the final syllable commit

Root cause

TextInput used self.current to ignore the next controlled value update after internal edits. When a Korean IME final syllable and Enter arrived together, the parent cleared the value after submit, but the component still treated that clear as its own echo and kept the final syllable in the internal buffer.

Closes #38117.

Verification

• npm test -- --run src/__tests__/textInputSubmitClear.test.tsx src/__tests__/textInputFastEcho.test.ts src/__tests__/textInputCursorSourceOfTruth.test.ts src/lib/editor.test.ts in ui-tui (41 passed)
• npx eslint src/components/textInput.tsx src/__tests__/textInputSubmitClear.test.tsx in ui-tui (exit 0; existing react-compiler warning at textInput.tsx:898)
• git diff --check origin/main..HEAD

[teknium1]

Thanks for the focused regression fix. Current main still has the unconditional self-echo suppression at ui-tui/src/components/textInput.tsx:568-581, so a parent value="" update can be ignored whenever self.current remains set. The proposed equality check in PR commit 4df1b98e2afe distinguishes that external clear from the actual local echo, and the added Ink test exercises the final-Korean-syllable-plus-Enter sequence.

The PR branch is behind current main, but the current-main diff from its merge base does not touch this effect hunk; this should be a mechanical salvage.

Automated hermes-sweeper review.

[teknium1]

Thanks for this fix! It was salvaged into #86761 (cherry-picked onto current main with your authorship preserved in the commit history) and is now merged. Closing since the work has landed.