Update file upload limits to 2GB in backend and frontend components; refactor avatar utility functions for improved name handling.

backend/src/main/resources/application.yml

@@ -8,8 +8,8 @@ spring:
     name: datatool-backend
   servlet:
     multipart:
-      max-file-size: 100MB
-      max-request-size: 100MB
+      max-file-size: 2GB
+      max-request-size: 2GB
 
 # WebSocket / STOMP 基础配置占位，后续可扩展
 datatool:
@@ -20,7 +20,7 @@ datatool:
   # 文件上传存储与限制（大文件走 HTTP 上传/下载，避免 WebSocket 断连）
   transfer:
     upload-dir: ./data/uploads
-    max-file-size: 104857600   # 100MB
+    max-file-size: 2147483648   # 2GB
     room-expire-hours: 24
     cleanup-interval-ms: 3600000   # 定时过期清理间隔（毫秒），默认 1 小时