Monorepo skeleton, Prisma schema, core domain and services with tests

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

packages/db/tsconfig.json

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+{ "extends": "../../tsconfig.base.json", "compilerOptions": { "types": ["node"] }, "include": ["src", "prisma.config.ts"] }