fix: preserve Korean heading word boundaries

[recrack]

Summary

• keep Korean headings from breaking inside words
• cap the Korean hero heading at a desktop-specific maximum while preserving the existing mobile size
• lock both behaviors into the public homepage design contract

Visual result

The reported sentence now groups naturally:

• 코딩 에이전트가
• 만든 iOS 앱을
• 내 iPhone에서
• 계속 사용하세요.

At 320 px the sentence uses five lines without splitting a word or overflowing.

Verification

• observed the contract fail before each production rule
• Scripts/test-public-homepage-design.sh
• Scripts/validate-product-hunt-site.sh
• Scripts/test-public-site-validator.sh
• Scripts/test-pages-publication.sh
• Scripts/validate-public-source.sh
• shellcheck, actionlint, and git diff --check
• Chromium at 320, 375, 390, 768, 1040, and 1440 px across all four locales

Refs #14

The issue will be closed only after the master Pages deployment and live Korean route are verified.