Switch release workflows from Yarn to npm

[aasimkhan30]

Summary

• replace Yarn with npm across package scripts, CI, release automation, and publishing docs
• add package-lock.json, use cached npm ci installs, and remove yarn.lock
• modernize release creation with the GitHub CLI and deterministic package extraction
• trigger automatic releases only for package.json changes on main, with an early exact-tag guard and manual dispatch retained

Validation

• npm ci
• npm run build
• npm run lint
• npm test
• npm pack --dry-run

The install reports the repository's existing dependency audit findings: 1 moderate and 16 high vulnerabilities.