Fix strategy checklist print closing too early.

Stop auto-closing the print tab on afterprint (short checklist pages were especially fragile), load print HTML via fetch into a blank window, and use CSS checkboxes instead of Unicode ballot boxes.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_hub_strategy_lib.py

@@ -33,16 +33,19 @@ class TestHubStrategyLib(unittest.TestCase):
     def test_export_html_contains_checklist(self):
         html = build_export_html("gate")
         self.assertIn("Gate", html)
-        self.assertIn("☐", html)
+        self.assertIn('class="box"', html)
+        self.assertNotIn("☐", html)
 
     def test_print_html_doc_and_checklist(self):
         doc = build_print_html("binance", "doc")
         cl = build_print_html("binance", "checklist")
         self.assertIn("window.print", doc)
         self.assertIn("window.print", cl)
+        self.assertNotIn("window.close", cl)
         self.assertIn("币安", doc)
         self.assertIn("开仓检查清单", cl)
-        self.assertIn("☐", cl)
+        self.assertIn('class="box"', cl)
+        self.assertIn("本账户仅做多", cl)
 
 
 if __name__ == "__main__":