build: establish TypeScript quality foundation

[fabiorosa]

What changed

• added an npm workspace with strict TypeScript configuration
• established API, worker, console, domain, and contracts boundaries without product behavior
• added Prettier, ESLint, Vitest, typecheck, and build gates under one root command
• added GitHub Actions using the committed lockfile
• documented Node.js 22, local verification, backlog status, and session state

Why

This creates a separate, reviewable engineering baseline before AfterHook
begins its first vertical product slice. The empty boundaries preserve the
intended architecture without introducing speculative webhook behavior or
infrastructure.

Validation

• npm ci
• npm run quality
• npm audit reports 0 vulnerabilities

Closes #1