feat(01-01): Prisma schema with Tenant/User models and Vitest test setup
- prisma/schema.prisma with Tenant, User, Role, TenantStatus models
- tenantId on all tenant-scoped models (RLS-ready convention)
- @@unique([email, tenantId]) and @@index([tenantId]) on User
- Grace period fields on Tenant (suspendedAt, gracePeriodEndsAt)
- RLS comment block documenting tenantId convention for future models
- src/lib/prisma.ts singleton PrismaClient pattern (hot-reload safe)
- vitest.config.ts with node environment and @/* path alias
- src/lib/__tests__/setup.test.ts smoke test (2 tests passing)
- package.json scripts: test, test:watch, db:push, db:generate, db:studio
- Schema synced to PostgreSQL 16 via prisma db push
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