docs: add launch plan and interest-signal tracking

[jinyounghub]

Closes #28

Summary

• Adds v0.2.0 launch notes and feedback-oriented announcement snippets.
• Adds interest-signal tracking guidance for GitHub traffic, npm downloads, and public engagement.
• Documents suggested GitHub topics and social preview checklist.
• Links launch, interest-signal, and metrics docs from the README.
• 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.