fix: harden public navigation state coverage

[Gnaroshi]

Summary

• move mobile locale controls into the navigation drawer to prevent untranslated-state header overlap
• enforce exactly one semantic and visual Reading current state
• validate stale/future current-focus boundaries
• exercise EN/KO translation fallbacks against real single-locale feed fixtures

Verification

• npm run content:check
• npm run check
• npm run build
• npm run check:i18n
• npm run check:public-tone
• npm run check:launch-content
• npm run check:links
• npm run test:smoke
• npm run test:feed-contract
• npm run test:e2e
• npm run test:a11y
• npm run test:visual
• npm run media:check
• npm run check:project-readiness
• npm run check:project-copy