fix: improve AdSense content quality signals

[moony01]

Summary

• add an editorial standards page with source, authorship, update, correction, and ranking context
• publish only source-backed, MEARROW-contextual news through the list, detail routes, sitemap, public API, and Workers assets
• add source/byline/update metadata and external-link safety to news pages
• align supported locale copy and make the editorial footer link wrap on mobile

AdSense rationale

AdSense review identified mearrow.com as 가치가 별로 없는 콘텐츠. This change removes thin/unattributed news from the public crawl surface and makes provenance and editorial context explicit for the remaining articles.

Verification

• pnpm lint (0 errors; existing warnings remain)
• pnpm test --run (38 files, 158 tests passed)
• pnpm exec tsc --noEmit
• pnpm build
• pnpm workers:build
• Playwright desktop/mobile route checks; held article returns 404 and mobile editorial page has no horizontal overflow