Improve Korean keep-all mixed-script breaks

[doyoon530]

Summary

• Improves wordBreak: keep-all for Korean-heavy mixed-script tokens.
• Keeps Hangul + ASCII/digit product-like runs together, e.g. AI정보공학과, README카드생성기, api문서v2가이드, 2026학년도공지.
• Stops keep-all continuation across path/query/key-value separators like /, ?, &, =, and :. These separators are treated as structural boundaries so URL/path/query/key-value text does not get folded into one Korean token.
• Adds regression tests for compact Korean tokens, separator boundaries, punctuation, and ZWSP.

Before / After

Before, ASCII-leading Korean tokens could stay split at the script boundary:

• AI정보공학과 -> AI + 정보공학과
• 2026학년도공지 -> 2026 + 학년도공지

After, compact Korean mixed-script tokens stay together under keep-all, while structured separators remain break boundaries:

• AI정보공학과 stays as one text unit
• key=value한글 remains split around =
• docs/README한글가이드 remains split around /

Testing

• bun test src/layout.test.ts
• bun run check
• bun test