feat(server): Go 模块骨架 + 工具链 [tsk_L2k2VrEujof8]

新建 server/ Go 模块：
- go.mod: module github.com/wangjia/pangolin/server, Go 1.22
  依赖: go-chi/chi/v5, google/uuid
- tools.go: //go:build tools 锁定 oapi-codegen / golang-migrate 版本
- cmd/server/main.go: chi router + GET /healthz → {"status":"ok"}，监听 :8080
- cmd/migrate/main.go: 占位入口（实逻辑归 1e）
- internal/{config,store,apierr,idgen,auth,codes,devices,nodes,usage,admin}/doc.go
  各包职责说明
- Makefile: build/test/vet/lint/generate/migrate-up/migrate-down
- .golangci.yml: govet/errcheck/staticcheck/revive/gofmt 基线
- README.md: 定位 + 目录树 + make 入口说明
- setup.sh: 首次 go mod tidy 引导脚本（go.sum 需运行后生成）

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

server/cmd/migrate/main.go

@@ -0,0 +1,14 @@
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func main() {
+	fmt.Fprintln(os.Stdout, "pangolin-migrate: database migration tool")
+	fmt.Fprintln(os.Stdout, "Usage: migrate [-up|-down] [-steps N]")
+	fmt.Fprintln(os.Stdout, "")
+	fmt.Fprintln(os.Stdout, "  (implementation in task 1e)")
+	os.Exit(0)
+}