fix: 适配网站结构更新

1. 标记已读改用预览通道 (download2.ashx)
2. 截图优先直接访问目标页面，避免 iframe 加载问题

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

services/screenshots.py

@@ -311,7 +311,14 @@ def take_screenshot_for_account(
                 screenshot_path = os.path.join(SCREENSHOTS_DIR, screenshot_filename)
 
                 cookies_for_shot = cookie_path if is_cookie_jar_fresh(cookie_path) else None
+                # 优先直接截取目标页面（center.aspx?bz=X），避免 iframe 加载问题
                 if take_screenshot_wkhtmltoimage(
+                    target_url,
+                    screenshot_path,
+                    cookies_path=cookies_for_shot,
+                    proxy_server=proxy_server,
+                    log_callback=custom_log,
+                ) or take_screenshot_wkhtmltoimage(
                     index_url,
                     screenshot_path,
                     cookies_path=cookies_for_shot,
@@ -319,12 +326,6 @@ def take_screenshot_for_account(
                     run_script=run_script,
                     window_status="ready",
                     log_callback=custom_log,
-                ) or take_screenshot_wkhtmltoimage(
-                    target_url,
-                    screenshot_path,
-                    cookies_path=cookies_for_shot,
-                    proxy_server=proxy_server,
-                    log_callback=custom_log,
                 ):
                     if os.path.exists(screenshot_path) and os.path.getsize(screenshot_path) > 1000:
                         log_to_client(f"✓ 截图成功: {screenshot_filename}", user_id, account_id)