feat: 站点访问统计与可配置侧边栏组件

- 新增访问统计：visitstats 服务与查询、visit_capture 中间件、爬虫/来源识别、管理端 analytics 页面
- 新增侧边栏：sidebar 服务与 handler、管理端 sidebar 配置页、前端侧边栏组件
- 新增 widget 嵌入代码生成（widgetCode）与 widgetApi
- 遥测逻辑迁移至 handler 层，删除 service/telemetry
- env 示例补充 Docker 部署可信代理 IP 说明

backend/service/setting.go

@@ -53,6 +53,10 @@ const (
 	SettingKeyAttachmentMaxCount = "attachment_max_count"
 	// SettingKeyImageMaxMB 正文插图上限（MB）；缺行=5
 	SettingKeyImageMaxMB = "image_max_mb"
+	// SettingKeyAnalyticsEnabled 访问统计采集开关；缺行视为开启（默认开）
+	SettingKeyAnalyticsEnabled = "analytics_enabled"
+	// SettingKeyAnalyticsRetentionDays 访问明细保留天数；缺行=90
+	SettingKeyAnalyticsRetentionDays = "analytics_retention_days"
 )
 
 const (
@@ -74,6 +78,10 @@ const (
 	MinAttachmentMaxCount     = 1
 	MaxAttachmentMaxCount     = 20
 	MaxAttachmentExtCount     = 80
+
+	DefaultAnalyticsRetentionDays = 90
+	MinAnalyticsRetentionDays     = 7
+	MaxAnalyticsRetentionDays     = 365
 )
 
 // DefaultAttachmentExts 论坛向默认允许扩展名（含安装包/脚本/网页）
@@ -880,3 +888,47 @@ func (s *SettingService) ImageMaxBytes() (int64, error) {
 	}
 	return int64(mb) << 20, nil
 }
+
+// AnalyticsEnabled 访问统计采集开关。缺行视为开启。
+func (s *SettingService) AnalyticsEnabled() (bool, error) {
+	v, found, err := s.getValue(SettingKeyAnalyticsEnabled)
+	if err != nil {
+		return true, err
+	}
+	return parseBoolDefaultTrue(v, found), nil
+}
+
+// SetAnalyticsEnabled 持久化采集开关；开启时删键保持「缺行=默认开」。
+func (s *SettingService) SetAnalyticsEnabled(on bool) error {
+	return s.setBoolDefaultTrue(SettingKeyAnalyticsEnabled, on)
+}
+
+// AnalyticsRetentionDays 访问明细保留天数。缺行=90；钳制 7–365。
+func (s *SettingService) AnalyticsRetentionDays() (int, error) {
+	v, found, err := s.getValue(SettingKeyAnalyticsRetentionDays)
+	if err != nil {
+		return DefaultAnalyticsRetentionDays, err
+	}
+	if !found {
+		return DefaultAnalyticsRetentionDays, nil
+	}
+	n, convErr := strconv.Atoi(strings.TrimSpace(v))
+	if convErr != nil || n < MinAnalyticsRetentionDays {
+		return DefaultAnalyticsRetentionDays, nil
+	}
+	if n > MaxAnalyticsRetentionDays {
+		return MaxAnalyticsRetentionDays, nil
+	}
+	return n, nil
+}
+
+// SetAnalyticsRetentionDays 持久化保留天数；等于默认值时删键。
+func (s *SettingService) SetAnalyticsRetentionDays(days int) error {
+	if days < MinAnalyticsRetentionDays || days > MaxAnalyticsRetentionDays {
+		return ErrInvalidSiteSetting
+	}
+	if days == DefaultAnalyticsRetentionDays {
+		return s.deleteKey(SettingKeyAnalyticsRetentionDays)
+	}
+	return s.putValue(SettingKeyAnalyticsRetentionDays, strconv.Itoa(days))
+}