Cross-platform development rulebook -- security (validation, auth tokens, passkeys/WebAuthn, API security, XSS/CSP, secrets), architecture (client-server, REST vs GraphQL, offline-first, monolith-first, CI/CD), and performance (bundles, images, Core Web Vitals, SSR/SSG, CDN caching) for SPA, PWA, mobile, Electron (with Fuses + asar integrity), and Tauri; includes /platform-review standalone command