重构日志与可观测性体系

新增单行文本编码器与结构化 GORM 日志，统一错误记录与请求日志策略，收紧日志文件权限并修复按天切分与压缩，支付回调参数脱敏，生产强制阿里云短信，RequestID 校验防注入，日志文案中文化。

backend/internal/database/mysql.go

@@ -1,19 +1,16 @@
 package database
 
 import (
-	"log"
-	"os"
-	"strings"
 	"time"
 
+	"go.uber.org/zap"
 	"gorm.io/driver/mysql"
 	"gorm.io/gorm"
-	"gorm.io/gorm/logger"
 )
 
-func OpenMySQL(dsn string, logLevel string) (*gorm.DB, error) {
+func OpenMySQL(dsn string, logLevel string, appLogger *zap.Logger) (*gorm.DB, error) {
 	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{
-		Logger: newGormLogger(logLevel),
+		Logger: newGormLogger(logLevel, appLogger),
 	})
 	if err != nil {
 		return nil, err
@@ -31,19 +28,3 @@ func OpenMySQL(dsn string, logLevel string) (*gorm.DB, error) {
 
 	return db, nil
 }
-
-func newGormLogger(logLevel string) logger.Interface {
-	level := logger.Warn
-	if strings.EqualFold(strings.TrimSpace(logLevel), "debug") {
-		level = logger.Info
-	}
-	return logger.New(
-		log.New(os.Stdout, "\r\n", log.LstdFlags),
-		logger.Config{
-			SlowThreshold:             500 * time.Millisecond,
-			LogLevel:                  level,
-			IgnoreRecordNotFoundError: true,
-			Colorful:                  false,
-		},
-	)
-}