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.

vite-frontend/src/api/index.ts

@@ -285,3 +285,11 @@ export const exportBackup = async (types: string[] = []) => {
 
 export const importBackup = (data: { types: string[]; [key: string]: any }) =>
   Network.post("/backup/import", data);
+
+export interface AnnouncementData {
+  content: string;
+  enabled: number;
+}
+
+export const getAnnouncement = () => Network.get<AnnouncementData>("/announcement/get");
+export const updateAnnouncement = (data: AnnouncementData) => Network.post("/announcement/update", data);