feat: add avatar photo upload via Huihui filecenter

- Add POST /avatars/{id}/upload-photo endpoint
- Use Huihui platform's filecenter API for image upload (same signing mechanism as news_service)
- Add upload button in avatar list table
- Frontend: handleUploadPhoto function with el-upload component
- Updates avatar photo_url in SQLite after successful upload

frontend/src/api/index.js

@@ -90,6 +90,9 @@ export const tailLogFile = (filename, lines = 100) => request.get(`/logs/files/$
 export const getAvatars = (params) => request.get('/avatars', { params })
 export const getAvatarDetail = (id) => request.get(`/avatars/${id}`)
 export const updateAvatarStatus = (id, status) => request.put(`/avatars/${id}/status`, { status })
+export const uploadAvatarPhoto = (id, formData) => request.post(`/avatars/${id}/upload-photo`, formData, {
+  headers: { 'Content-Type': 'multipart/form-data' }
+})
 
 export default request
 export const uploadAvatar = (userId, formData) => request.post(`/users/${userId}/upload-avatar`, formData, { headers: { "Content-Type": "multipart/form-data" } })