feat: 新增 Docker Compose 部署方案

- Dockerfile 单阶段 Alpine 镜像，使用国内镜像（npmmirror / Prisma 引擎 / apk）加速
- entrypoint 首次复制内置图章素材到 uploads volume，自动执行 prisma migrate deploy
- docker-compose.yml 绑定 127.0.0.1:3001，强制走外部 Nginx 反代
- Express 在 production 下同时托管 packages/web/dist 及 SPA fallback
- Prisma schema 增加 linux-musl 二进制目标，支持 Alpine 运行
- 新增 DEPLOY.md 部署指南，含 .env 模板与 Nginx 反代示例

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docker/entrypoint.sh

@@ -0,0 +1,20 @@
+#!/bin/sh
+set -e
+
+cd /app
+
+mkdir -p /app/data
+mkdir -p /app/packages/server/uploads/stamps
+
+# Seed stamp assets on first run (idempotent)
+if [ -z "$(ls -A /app/packages/server/uploads/stamps 2>/dev/null)" ]; then
+  echo "→ Seeding stamp assets into uploads volume..."
+  cp /app/stamps-seed/*.jpg /app/packages/server/uploads/stamps/ 2>/dev/null || true
+fi
+
+echo "→ Applying database migrations..."
+pnpm exec prisma migrate deploy
+
+echo "→ Starting server on :${SERVER_PORT:-3000}..."
+cd /app/packages/server
+exec pnpm exec tsx src/index.ts