Next.js SaaS 应用的 AGENTS.md 规则

# Project Rules

## Stack
- Next.js (App Router) + TypeScript (strict).
- Tailwind CSS v4. No CSS-in-JS.
- PostgreSQL via the existing db client in `src/lib/db.ts`.

## Hard rules
- Never add a dependency without listing it and why first.
- Server Components by default. Only add `"use client"` when you need state,
  effects, or browser APIs — and keep those components small.
- All env vars go through `src/lib/env.ts` (zod-validated). Never read
  `process.env` directly in app code.
- Never put secrets or server-only code in a Client Component.

## Conventions
- Co-locate route code under `app/`. Shared logic lives in `src/lib/`.
- Use the existing UI primitives in `src/components/ui/` before adding new ones.
- Write the diff and wait for approval before editing more than 3 files.

## Definition of done
- `bun run typecheck` and `bun run lint` pass.
- No new `any`. No unused exports.