feat: refactor PDF extraction to caption-based screenshots, add upvote refresh, clean up UI

- PDF extractor: rewrite from embedded bitmap extraction to caption-based
  page region screenshots. Finds Figure/Table captions via regex,截取上方/下方
  page region, handles compound figures and vector graphics.
- Upvote refresh: new crawler.refresh_upvotes() re-fetches upvotes for recent
  N days without inserting new papers. Scheduler runs daily 30min after pipeline.
- Admin: add /admin/refresh-upvotes endpoint and dashboard button.
- UI: remove date quick nav, show upvote update time on detail/card pages,
  clean up CSS date-chip styles.
- Utils: add recent_date_strs() helper.

app/routes/pages.py

@@ -315,11 +315,16 @@ def _link_figures_with_images(
     fig_type_unmatched = [f for f in unmatched if _is_figure_type(f.get("id", ""))]
     table_type_unmatched = [f for f in unmatched if not _is_figure_type(f.get("id", ""))]
 
-    # 提取的图片也按类型分流，按文件名排序
+    # 提取的图片按类型分流，按文件名中的编号排序
     def _sort_key(name: str) -> tuple[int, int]:
-        m = re.search(r'page(\d+)_(?:img|table)(\d+)', name)
+        # 新格式：figure_1.png, table_1.png
+        m = re.search(r'(?:figure|table)_(\d+)', name)
         if m:
-            return (int(m.group(1)), int(m.group(2)))
+            return (0, int(m.group(1)))
+        # 旧格式：page2_img1.png, page5_table1.png
+        m2 = re.search(r'page(\d+)_(?:img|table)(\d+)', name)
+        if m2:
+            return (int(m2.group(1)), int(m2.group(2)))
         return (0, 0)
 
     fig_images = sorted(