修复帖内 CSS 污染整页：前后端禁止 style 并消毒 HTML。

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

go.mod

@@ -8,6 +8,7 @@ require (
 	github.com/glebarez/sqlite v1.11.0
 	github.com/golang-jwt/jwt/v5 v5.2.1
 	github.com/kardianos/service v1.2.2
+	github.com/microcosm-cc/bluemonday v1.0.27
 	github.com/minio/minio-go/v7 v7.0.98
 	golang.org/x/crypto v0.46.0
 	golang.org/x/image v0.44.0
@@ -16,6 +17,7 @@ require (
 )
 
 require (
+	github.com/aymerick/douceur v0.2.0 // indirect
 	github.com/bytedance/sonic v1.11.6 // indirect
 	github.com/bytedance/sonic/loader v0.1.1 // indirect
 	github.com/cloudwego/base64x v0.1.4 // indirect
@@ -30,6 +32,7 @@ require (
 	github.com/go-playground/validator/v10 v10.20.0 // indirect
 	github.com/goccy/go-json v0.10.2 // indirect
 	github.com/google/uuid v1.6.0 // indirect
+	github.com/gorilla/css v1.0.1 // indirect
 	github.com/jinzhu/inflection v1.0.0 // indirect
 	github.com/jinzhu/now v1.1.5 // indirect
 	github.com/json-iterator/go v1.1.12 // indirect