fix: 支持直接运行 server/app.py，统一导入方式

server/app.py

@@ -1,12 +1,17 @@
 import os
+import sys
 
 from flask import Flask, jsonify, request, send_from_directory, session
 
-from .auth import admin_required, authenticate, create_user, login_required
-from .db import BASE_DIR, get_db, init_db
-from .entries_api import entries_bp
-from .settings_api import settings_bp
-from .vocab_api import vocab_bp
+ROOT_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+if ROOT_DIR not in sys.path:
+    sys.path.insert(0, ROOT_DIR)
+
+from server.auth import admin_required, authenticate, create_user, login_required
+from server.db import BASE_DIR, get_db, init_db
+from server.entries_api import entries_bp
+from server.settings_api import settings_bp
+from server.vocab_api import vocab_bp
 
 
 def create_app():