feat: 社区准则改为数据库存储

- AuthController 注入 SiteSettings 依赖，RegisterPage 优先从 DB 读取准则
- DB 中 site.guidelines 为空时 fallback 到静态 guidelines.html 文件
- 管理后台站点设置页新增「内容管理」分区，textarea 编辑社区准则
- 添加准则编辑区垂直布局样式

internal/controller/auth_controller.go

@@ -1,6 +1,7 @@
 package controller
 
 import (
+	"html/template"
 	"net/http"
 
 	"metazone.cc/metalab/internal/common"
@@ -17,11 +18,12 @@ type AuthController struct {
 	sessionManager *session.Manager
 	rateLimiter    rateLimiter
 	cfg            *config.Config
+	siteSettings   *config.SiteSettings
 }
 
 // NewAuthController 构造函数
-func NewAuthController(authService authUseCase, sm *session.Manager, limiter rateLimiter, cfg *config.Config) *AuthController {
-	return &AuthController{authService: authService, sessionManager: sm, rateLimiter: limiter, cfg: cfg}
+func NewAuthController(authService authUseCase, sm *session.Manager, limiter rateLimiter, cfg *config.Config, siteSettings *config.SiteSettings) *AuthController {
+	return &AuthController{authService: authService, sessionManager: sm, rateLimiter: limiter, cfg: cfg, siteSettings: siteSettings}
 }
 
 // RegisterPage 注册页面（已登录用户重定向到首页）
@@ -30,10 +32,18 @@ func (ac *AuthController) RegisterPage(c *gin.Context) {
 		c.Redirect(http.StatusFound, "/")
 		return
 	}
-	guidelines, err := theme.LoadContent("templates/MetaLab-2026/guidelines.html")
-	if err != nil {
-		c.String(http.StatusInternalServerError, "加载准则失败")
-		return
+	// 优先从 DB 读取社区准则，为空时 fallback 到静态文件
+	guidelinesHTML := ac.siteSettings.Get("site.guidelines", "")
+	var guidelines template.HTML
+	if guidelinesHTML != "" {
+		guidelines = template.HTML(guidelinesHTML)
+	} else {
+		content, err := theme.LoadContent("templates/MetaLab-2026/guidelines.html")
+		if err != nil {
+			c.String(http.StatusInternalServerError, "加载准则失败")
+			return
+		}
+		guidelines = content
 	}
 	c.HTML(http.StatusOK, "auth/register.html", common.BuildPageData(c, gin.H{
 		"Title":               "注册",