新增公告中心功能

## 功能概述
在钱包旁边新增公告中心，用户可以查看平台通知、教程、规则和常见问题。

## 主要变更

### 后端
- 新增 announcement 模块（handler/service/repository）
- 新增 announcements 数据库表
- 添加公告相关 API 端点（用户端和管理端）
- 扩展 response 包，新增 NotFound 和 InternalServerError 方法

### 前端
- 新增公告功能模块（/features/announcement）
- 实现公告列表页和详情页
- 在顶部导航添加公告入口（钱包旁边）
- 支持按分类筛选（通知、教程、规则、FAQ）
- 支持置顶和重要标记显示

### 数据库
- 迁移文件：000005_add_announcements.sql
- 示例数据：000006_insert_sample_announcements.sql
- 包含6条示例公告

## 技术特点
- 遵循项目现有架构模式
- 响应式设计，支持移动端
- 自动统计浏览次数
- 支持富文本内容展示

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/internal/router/router.go

@@ -13,6 +13,7 @@ import (
 	"hfb_sys/backend/internal/modules/adminmgr"
 	"hfb_sys/backend/internal/modules/adminrole"
 	"hfb_sys/backend/internal/modules/adminuser"
+	"hfb_sys/backend/internal/modules/announcement"
 	"hfb_sys/backend/internal/modules/auth"
 	"hfb_sys/backend/internal/modules/chat"
 	"hfb_sys/backend/internal/modules/chathub"
@@ -183,6 +184,12 @@ func New(cfg config.Config, deps Dependencies, logger *zap.Logger) *gin.Engine {
 	fileHandler := filemodule.NewHandler(fileService, fileStorage)
 	listingService := listing.NewService(listingRepo, systemConfigRepo)
 	listingHandler := listing.NewHandler(listingService, fileStorage)
+	var announcementRepo *announcement.Repository
+	if deps.DB != nil {
+		announcementRepo = announcement.NewRepository(deps.DB)
+	}
+	announcementService := announcement.NewService(announcementRepo)
+	announcementHandler := announcement.NewHandler(announcementService)
 	requireAuth := middleware.Auth(jwtManager)
 	requireAdmin := middleware.AdminAuth(jwtManager)
 	requireRealname := middleware.RequireRealname(userRepo)
@@ -307,6 +314,12 @@ func New(cfg config.Config, deps Dependencies, logger *zap.Logger) *gin.Engine {
 			realnameRoutes.GET("/status", realnameHandler.Status)
 		}
 
+		announcementRoutes := api.Group("/announcements")
+		{
+			announcementRoutes.GET("", announcementHandler.List)
+			announcementRoutes.GET("/:id", announcementHandler.GetByID)
+		}
+
 		adminAuthRoutes := api.Group("/admin/auth")
 		{
 			adminAuthRoutes.GET("/captcha", adminAuthHandler.Captcha)
@@ -381,6 +394,15 @@ func New(cfg config.Config, deps Dependencies, logger *zap.Logger) *gin.Engine {
 			adminRoutes.DELETE("/admin-users/:id", requirePerm("admin_user:manage"), adminMgrHandler.Delete)
 			adminRoutes.PUT("/admin-users/:id/roles", requirePerm("admin_user:manage"), adminMgrHandler.AssignRoles)
 			adminRoutes.PUT("/admin-users/:id/password", adminMgrHandler.ChangePassword)
+
+			// 公告管理
+			adminRoutes.GET("/announcements", requirePerm("announcement:view"), announcementHandler.AdminList)
+			adminRoutes.GET("/announcements/:id", requirePerm("announcement:view"), announcementHandler.AdminGetByID)
+			adminRoutes.POST("/announcements", requirePerm("announcement:manage"), announcementHandler.Create)
+			adminRoutes.PUT("/announcements/:id", requirePerm("announcement:manage"), announcementHandler.Update)
+			adminRoutes.POST("/announcements/:id/publish", requirePerm("announcement:manage"), announcementHandler.Publish)
+			adminRoutes.POST("/announcements/:id/archive", requirePerm("announcement:manage"), announcementHandler.Archive)
+			adminRoutes.DELETE("/announcements/:id", requirePerm("announcement:manage"), announcementHandler.Delete)
 		}
 	}