refactor: main.go 서버 초기화 로직을 internal/server/server.go로 분리

Fiber 앱 설정, 미들웨어, rate limiter를 server 패키지로 추출.
main.go는 DB 연결, DI, 서버 시작, graceful shutdown만 담당.

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

internal/server/server.go

@@ -0,0 +1,110 @@
+package server
+
+import (
+	"strconv"
+	"time"
+
+	"a301_server/pkg/apperror"
+	"a301_server/pkg/metrics"
+	"a301_server/pkg/middleware"
+
+	"github.com/gofiber/fiber/v2"
+	"github.com/gofiber/fiber/v2/middleware/cors"
+	"github.com/gofiber/fiber/v2/middleware/limiter"
+	"github.com/gofiber/fiber/v2/middleware/logger"
+	"github.com/redis/go-redis/v9"
+	"gorm.io/gorm"
+)
+
+// New creates a configured Fiber app with all global middleware applied.
+func New() *fiber.App {
+	app := fiber.New(fiber.Config{
+		StreamRequestBody: true,
+		BodyLimit:         4 * 1024 * 1024 * 1024, // 4GB
+		ErrorHandler:      middleware.ErrorHandler,
+	})
+	app.Use(middleware.RequestID)
+	app.Use(middleware.Metrics)
+	app.Get("/metrics", metrics.Handler)
+	app.Use(logger.New(logger.Config{
+		Format:     `{"time":"${time}","status":${status},"latency":"${latency}","method":"${method}","path":"${path}","ip":"${ip}","reqId":"${locals:requestID}"}` + "\n",
+		TimeFormat: "2006-01-02T15:04:05Z07:00",
+	}))
+	app.Use(middleware.SecurityHeaders)
+	app.Use(cors.New(cors.Config{
+		AllowOrigins:     "https://a301.tolelom.xyz",
+		AllowHeaders:     "Origin, Content-Type, Authorization, Idempotency-Key, X-API-Key",
+		AllowMethods:     "GET, POST, PUT, PATCH, DELETE",
+		AllowCredentials: true,
+	}))
+	return app
+}
+
+// AuthLimiter returns a rate limiter for auth endpoints (10 req/min per IP).
+func AuthLimiter() fiber.Handler {
+	return limiter.New(limiter.Config{
+		Max:        10,
+		Expiration: 1 * time.Minute,
+		KeyGenerator: func(c *fiber.Ctx) string {
+			return c.IP()
+		},
+		LimitReached: func(c *fiber.Ctx) error {
+			return apperror.ErrRateLimited
+		},
+	})
+}
+
+// APILimiter returns a rate limiter for general API endpoints (60 req/min per IP).
+func APILimiter() fiber.Handler {
+	return limiter.New(limiter.Config{
+		Max:        60,
+		Expiration: 1 * time.Minute,
+		KeyGenerator: func(c *fiber.Ctx) string {
+			return c.IP()
+		},
+		LimitReached: func(c *fiber.Ctx) error {
+			return apperror.ErrRateLimited
+		},
+	})
+}
+
+// ChainUserLimiter returns a rate limiter for chain transactions (20 req/min per user).
+func ChainUserLimiter() fiber.Handler {
+	return limiter.New(limiter.Config{
+		Max:        20,
+		Expiration: 1 * time.Minute,
+		KeyGenerator: func(c *fiber.Ctx) string {
+			if uid, ok := c.Locals("userID").(uint); ok {
+				return "chain_user:" + strconv.FormatUint(uint64(uid), 10)
+			}
+			return "chain_ip:" + c.IP()
+		},
+		LimitReached: func(c *fiber.Ctx) error {
+			return apperror.ErrRateLimited
+		},
+	})
+}
+
+// HealthCheck returns a handler that reports server liveness.
+func HealthCheck() fiber.Handler {
+	return func(c *fiber.Ctx) error {
+		return c.JSON(fiber.Map{"status": "ok"})
+	}
+}
+
+// ReadyCheck returns a handler that verifies DB and Redis connectivity.
+func ReadyCheck(db *gorm.DB, rdb *redis.Client) fiber.Handler {
+	return func(c *fiber.Ctx) error {
+		sqlDB, err := db.DB()
+		if err != nil {
+			return c.Status(fiber.StatusServiceUnavailable).JSON(fiber.Map{"status": "error", "detail": "db pool"})
+		}
+		if err := sqlDB.Ping(); err != nil {
+			return c.Status(fiber.StatusServiceUnavailable).JSON(fiber.Map{"status": "error", "detail": "db"})
+		}
+		if err := rdb.Ping(c.Context()).Err(); err != nil {
+			return c.Status(fiber.StatusServiceUnavailable).JSON(fiber.Map{"status": "error", "detail": "redis"})
+		}
+		return c.JSON(fiber.Map{"status": "ok"})
+	}
+}