feat: Add initialization progress WebSocket and UI components

- Implement WebSocket route for initialization progress updates
- Create initialization component with progress bar and stages
- Add styles for initialization UI
- Update base template to include initialization component
- Enhance model scanner to broadcast progress during initialization

py/routes/checkpoints_routes.py

@@ -428,15 +428,16 @@ class CheckpointsRoutes:
     async def handle_checkpoints_page(self, request: web.Request) -> web.Response:
         """Handle GET /checkpoints request"""
         try:
-            # 检查缓存初始化状态，根据initialize_in_background的工作方式调整判断逻辑
+            # Check if the CheckpointScanner is initializing
+            # It's initializing if the cache object doesn't exist yet,
+            # OR if the scanner explicitly says it's initializing (background task running).
             is_initializing = (
-                self.scanner._cache is None or 
-                len(self.scanner._cache.raw_data) == 0 or
-                hasattr(self.scanner, '_is_initializing') and self.scanner._is_initializing
+                self.scanner._cache is None or
+                (hasattr(self.scanner, '_is_initializing') and self.scanner._is_initializing)
             )
 
             if is_initializing:
-                # 如果正在初始化，返回一个只包含加载提示的页面
+                # If still initializing, return loading page
                 template = self.template_env.get_template('checkpoints.html')
                 rendered = template.render(
                     folders=[],  # 空文件夹列表