fix(config): validate DATABASE_URL required and parseable, log redis disabled (B15)

backend/internal/config/config.go

@@ -2,11 +2,14 @@ package config
 
 import (
 	"fmt"
+	"log"
 	"os"
 	"path/filepath"
 	"strconv"
 	"strings"
 	"time"
+
+	"github.com/jackc/pgx/v5/pgxpool"
 )
 
 type Config struct {
@@ -52,6 +55,18 @@ func Load() (*Config, error) {
 	if secret == "" {
 		return nil, fmt.Errorf("JWT_SECRET required")
 	}
+	// Validate required fields.
+	dbURL := env("DATABASE_URL", "")
+	if dbURL == "" {
+		return nil, fmt.Errorf("DATABASE_URL is required")
+	}
+	if _, perr := pgxpool.ParseConfig(dbURL); perr != nil {
+		return nil, fmt.Errorf("DATABASE_URL: %w", perr)
+	}
+	if env("REDIS_URL", "") == "" {
+		log.Printf("redis disabled: rate-limit/scan-lock/page-cache off")
+	}
+
 	// resolveDir: macOS 开发机上 /var、/tmp 是指向 /private 的软链,
 	// 启动时解析一次才能让 root_path 前缀校验对上真实路径;目录不存在/出错则保留原值(Docker 路径不受影响)
 	resolveDir := func(dir string) string {