docs: prepare v0.2 launch and discovery pack

[jinyounghub]

Closes #25

Summary

• Adds public v0.2.0 announcement notes with short, medium, and technical drafts.
• Improves first-screen README positioning for maintainers evaluating AI-agent GitHub Actions workflows.
• Expands npm keywords for discovery and documents suggested repository topics/social preview guidance.
• Adds a safe advisory-mode trial note to adoption docs.
• Keeps external adopters at 0 and avoids private application/benefit language.

Validation

• npm ci
• npm run lint
• npm test
• npm run build
• npm audit --audit-level=moderate
• npm pack --dry-run
• node dist/cli.js scan .github/workflows --format markdown --fail-on never
• node dist/cli.js scan tests/fixtures --format markdown --fail-on never
• node dist/cli.js scan examples --format markdown --fail-on never
• Restricted public phrase search: no restricted terms found

Release

• No npm publish in this PR.