feat(settings): 后台可开关全站评论

关闭后禁止新评论与回复，已有内容仍可浏览；设置经 WS 同步到前台。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/service/setting.go

@@ -20,6 +20,8 @@ const (
 	SettingKeySiteName             = "site_name"
 	SettingKeySiteDescription      = "site_description"
 	SettingKeyAllowRegister        = "allow_register"
+	// SettingKeyAllowComments 全站开放评论；缺行视为开启（默认开）
+	SettingKeyAllowComments     = "allow_comments"
 	SettingKeyPostCooldownHours = "post_cooldown_hours"
 	// SettingKeyCodeBlockAutoFold 代码块自动折叠；缺行视为开启
 	SettingKeyCodeBlockAutoFold = "code_block_auto_fold"
@@ -62,6 +64,7 @@ type PublicSiteSettings struct {
 	SiteName              string `json:"site_name"`
 	SiteDescription       string `json:"site_description"`
 	AllowRegister         bool   `json:"allow_register"`
+	AllowComments         bool   `json:"allow_comments"`
 	PostCooldownHours     int    `json:"post_cooldown_hours"`
 	CodeBlockAutoFold     bool   `json:"code_block_auto_fold"`
 	CodeBlockFoldLines    int    `json:"code_block_fold_lines"`
@@ -128,6 +131,7 @@ func (s *SettingService) Public() (PublicSiteSettings, error) {
 		SiteDescription:      DefaultSiteDescription,
 		TrustReviewedPublish: true,
 		AllowRegister:        true,
+		AllowComments:        true,
 		PostCooldownHours:    DefaultCooldownHours,
 		CodeBlockAutoFold:    true,
 		CodeBlockFoldLines:   DefaultCodeFoldLines,
@@ -173,6 +177,12 @@ func (s *SettingService) Public() (PublicSiteSettings, error) {
 	}
 	out.AllowRegister = parseBoolDefaultTrue(reg, found)
 
+	comments, err := s.AllowComments()
+	if err != nil {
+		return out, err
+	}
+	out.AllowComments = comments
+
 	hours, err := s.PostCooldownHours()
 	if err != nil {
 		return out, err
@@ -286,6 +296,19 @@ func (s *SettingService) SetAllowRegister(on bool) error {
 	return s.setBoolDefaultTrue(SettingKeyAllowRegister, on)
 }
 
+// AllowComments 是否允许全站发表评论/回复。缺行视为开启。
+func (s *SettingService) AllowComments() (bool, error) {
+	v, found, err := s.getValue(SettingKeyAllowComments)
+	if err != nil {
+		return true, err
+	}
+	return parseBoolDefaultTrue(v, found), nil
+}
+
+// SetAllowComments 持久化评论开关；开启时删键保持「缺行=默认开」。
+func (s *SettingService) SetAllowComments(on bool) error {
+	return s.setBoolDefaultTrue(SettingKeyAllowComments, on)
+}
 
 // PostCooldownHours 新用户发帖冷静期（小时）。缺行=24；0 表示关闭。
 func (s *SettingService) PostCooldownHours() (int, error) {