feat(backend): module scaffold, config, gin router with healthz

backend/internal/config/config.go

@@ -0,0 +1,54 @@
+package config
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"time"
+)
+
+type Config struct {
+	Addr          string
+	DatabaseURL   string
+	RedisURL      string
+	JWTSecret     []byte
+	AdminUser     string
+	AdminPassword string
+	BooksDir      string
+	CacheDir      string
+	ScanInterval  time.Duration
+	UploadMaxMB   int64
+}
+
+func Load() (*Config, error) {
+	env := func(k, def string) string {
+		if v := os.Getenv(k); v != "" {
+			return v
+		}
+		return def
+	}
+	scanSec, err := strconv.Atoi(env("SCAN_INTERVAL_SEC", "60"))
+	if err != nil {
+		return nil, fmt.Errorf("SCAN_INTERVAL_SEC: %w", err)
+	}
+	uploadMB, err := strconv.ParseInt(env("UPLOAD_MAX_MB", "200"), 10, 64)
+	if err != nil {
+		return nil, fmt.Errorf("UPLOAD_MAX_MB: %w", err)
+	}
+	secret := os.Getenv("JWT_SECRET")
+	if secret == "" {
+		return nil, fmt.Errorf("JWT_SECRET required")
+	}
+	return &Config{
+		Addr:          env("ADDR", ":8080"),
+		DatabaseURL:   env("DATABASE_URL", ""),
+		RedisURL:      env("REDIS_URL", ""),
+		JWTSecret:     []byte(secret),
+		AdminUser:     env("ADMIN_USER", ""),
+		AdminPassword: env("ADMIN_PASSWORD", ""),
+		BooksDir:      env("BOOKS_DIR", "/data/books"),
+		CacheDir:      env("CACHE_DIR", "/data/cache"),
+		ScanInterval:  time.Duration(scanSec) * time.Second,
+		UploadMaxMB:   uploadMB,
+	}, nil
+}