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/logging/text_encoder_test.go

@@ -0,0 +1,36 @@
+package logging
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+	"time"
+
+	"go.uber.org/zap"
+	"go.uber.org/zap/zapcore"
+)
+
+func TestTextEncoderProducesReadableSingleLine(t *testing.T) {
+	var output bytes.Buffer
+	core := zapcore.NewCore(newTextEncoder(time.UTC), zapcore.AddSync(&output), zapcore.DebugLevel)
+	logger := zap.New(core)
+	logger.Info("服务启动",
+		zap.String("request_id", "req-1"),
+		zap.String("empty", ""),
+		zap.String("detail", "line1\nline2"),
+	)
+
+	got := output.String()
+	if strings.ContainsAny(got, "{}") {
+		t.Fatalf("output should not use JSON object syntax: %s", got)
+	}
+	if !strings.Contains(got, "INFO  | 服务启动 | request_id=req-1") {
+		t.Fatalf("unexpected text output: %s", got)
+	}
+	if strings.Contains(got, "empty=") {
+		t.Fatalf("empty fields should be omitted: %s", got)
+	}
+	if strings.Count(got, "\n") != 1 || !strings.Contains(got, `detail="line1\nline2"`) {
+		t.Fatalf("output should remain one physical line: %q", got)
+	}
+}