feat(create-app): add CLI Scaffolder (3.1) — interactive product repo generator
Scaffolder (scaffolder.ts):
- Interactive prompts: product name/ID/tagline/domain, port, platforms, features
- --from product.json flag to skip prompts (non-interactive)
- --dry-run preview mode
- Generates backend (always) + web (Next.js) + mobile (Expo) based on selection
- Template engine with {{VARIABLE}} and {{#IF FEATURE}} conditional blocks
- Backend scaffold: Fastify 5, Zod config, JWT auth, datastore, server.ts
- Web scaffold: Next.js 16 App Router, layout, page, product-config
- Mobile scaffold: Expo with app.json, index screen
- Root files: product.json, .gitignore, .env.example, README.md
Tests: 26 passing (11 template-engine + 15 scaffolder)
Tested with ActionTrail product.json dry-run — correct output
6354711f97