feat: 添加公告系统（支持SQLite和PostgreSQL） (#129)

* feat(announcement): add database schema for SQLite and PostgreSQL

Add announcement table with id, title, content, enabled, created_at, updated_at columns to both SQLite and PostgreSQL schemas to support announcement system.

* feat(announcement): implement SQLite repository for announcement management

Add announcement CRUD operations in SQLite repository including create, read, update, delete, and list methods with proper error handling.

* feat(announcement): add HTTP handlers and auth middleware for announcement API

Implement admin-only update endpoint and public read endpoint for announcements. Add auth middleware to enforce admin-only access for update operations.

* feat(announcement): add frontend API client for announcement endpoints

Implement API client methods for fetching announcements and updating announcement settings with proper error handling.

* feat(announcement): add announcement display component to dashboard

Implement announcement display section in dashboard with real-time updates and proper styling using HeroUI components.

* feat(announcement): add announcement management UI to config page

Implement announcement settings panel with enable/disable toggle and content editor for admin users to manage announcements.

go-backend/internal/http/handler/handler.go

@@ -177,6 +177,8 @@ func (h *Handler) Register(mux *http.ServeMux) {
 	mux.HandleFunc("/api/v1/federation/runtime/diagnose", h.authPeer(h.federationRuntimeDiagnose))
 	mux.HandleFunc("/api/v1/federation/runtime/command", h.authPeer(h.federationRuntimeCommand))
 	mux.HandleFunc("/api/v1/federation/node/import", h.nodeImport)
+	mux.HandleFunc("/api/v1/announcement/get", h.getAnnouncement)
+	mux.HandleFunc("/api/v1/announcement/update", h.updateAnnouncement)
 
 	mux.HandleFunc("/flow/test", h.flowTest)
 	mux.HandleFunc("/flow/config", h.flowConfig)
@@ -1228,3 +1230,53 @@ func (h *Handler) backupImport(w http.ResponseWriter, r *http.Request) {
 	result.AutoBackup = autoBackup
 	response.WriteJSON(w, response.OK(result))
 }
+
+func (h *Handler) getAnnouncement(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodGet {
+		response.WriteJSON(w, response.ErrDefault("请求失败"))
+		return
+	}
+
+	ann, err := h.repo.GetAnnouncement()
+	if err != nil {
+		response.WriteJSON(w, response.Err(-1, fmt.Sprintf("获取公告失败: %v", err)))
+		return
+	}
+
+	if ann == nil {
+		response.WriteJSON(w, response.OK(map[string]interface{}{
+			"content": "",
+			"enabled": 0,
+		}))
+		return
+	}
+
+	response.WriteJSON(w, response.OK(map[string]interface{}{
+		"content": ann.Content,
+		"enabled": ann.Enabled,
+	}))
+}
+
+func (h *Handler) updateAnnouncement(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		response.WriteJSON(w, response.ErrDefault("请求失败"))
+		return
+	}
+
+	var req struct {
+		Content string `json:"content"`
+		Enabled int    `json:"enabled"`
+	}
+	if err := decodeJSON(r.Body, &req); err != nil {
+		response.WriteJSON(w, response.Err(500, "请求参数错误"))
+		return
+	}
+
+	now := time.Now().UnixMilli()
+	if err := h.repo.UpsertAnnouncement(req.Content, req.Enabled, now); err != nil {
+		response.WriteJSON(w, response.Err(-1, fmt.Sprintf("更新公告失败: %v", err)))
+		return
+	}
+
+	response.WriteJSON(w, response.OKEmpty())
+}