docs: add Zenn and DEV article drafts

[enumura1]

Summary

• add editorial notes recording the researched publishing guidance and fact-check checklist
• add a Japanese Zenn article draft focused on Web Speech word boundaries and inside-glyph rendering
• add an English DEV Community article draft focused on the rendering and timing trade-offs

Validation

• ./node_modules/.bin/prettier --check 'articles/**/*.md'
• npm run lint
• npm test
• npm run build
• npm run docs:build

The article drafts are not publication actions. The pre-publication checklist requires author review of first-person wording, manual browser/voice checks, and DEV's AI-assistance disclosure when applicable.