chore(env): drop root .env.example; clarify per-mode usage

- 删根 .env.example(误导:实际只在 docker-compose.prod.yml 模式被读取)
- README quick-start 改为从 apps/*/.env.example 复制(本地 dev 标准做法)
- docker-compose.prod.yml 顶部加注释列出它依赖的 root .env keys

之后两种模式职责清晰:
  systemd 模式 → apps/pac-service/.env + apps/pac-web/.env(唯一真相)
  compose 模式 → 根 .env(用户自己按 prod.yml 注释组装)

.env.example

-# --- Database ---
-DATABASE_URL=postgresql://pac:pac@localhost:5532/pac?schema=public
-
-# --- Redis ---
-REDIS_URL=redis://localhost:6479
-
-# --- JWT ---
-JWT_SECRET=replace-with-strong-random-secret-min-32-chars
-JWT_REFRESH_SECRET=replace-with-another-strong-secret-min-32-chars
-JWT_EXPIRES_IN=2h
-JWT_REFRESH_EXPIRES_IN=7d
-
-# --- AI Gateway ---
-# The gateway is a passthrough that mirrors the Dify API shape
-# (POST /workflows/run + /workflows/run with stream).
-AI_GATEWAY_URL=https://ai-gateway.example.com
-AI_GATEWAY_API_KEY=
-
-# --- Service ---
-NODE_ENV=development
-PORT=3101
-LOG_LEVEL=info
-CORS_ORIGINS=http://localhost:3100
-
-# --- One-time code ---
-EXCHANGE_CODE_TTL_SECONDS=60
-
-# --- Frontend ---
-NEXT_PUBLIC_API_BASE_URL=http://localhost:3101

README.md

@@ -45,8 +45,9 @@ Adapters (sync engine):
 # 1. install
 pnpm install
 
-# 2. start postgres + redis (and optionally the apps)
-cp .env.example .env
+# 2. start postgres + redis (apps will pick up apps/*/.env automatically)
+cp apps/pac-service/.env.example apps/pac-service/.env
+cp apps/pac-web/.env.example apps/pac-web/.env
 docker compose up -d postgres redis
 
 # 3. run the database migration + seed the demo platform

docker-compose.prod.yml

+# Requires a root `.env` next to this file. Keys it needs:
+#   POSTGRES_USER / POSTGRES_PASSWORD / POSTGRES_DB
+#   DATABASE_URL / REDIS_URL
+#   JWT_SECRET / JWT_REFRESH_SECRET / JWT_EXPIRES_IN / JWT_REFRESH_EXPIRES_IN
+#   AI_GATEWAY_URL / AI_GATEWAY_API_KEY
+#   CORS_ORIGINS / EXCHANGE_CODE_TTL_SECONDS
+#   NEXT_PUBLIC_API_BASE_URL  (build-time, change → rebuild web)
+# Per-key meaning: see apps/pac-service/.env.example (most overlap).
+# Run: docker compose -f docker-compose.prod.yml up -d --build
 services:
   postgres:
     image: postgres:16-alpine