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/services/scheduler.py

@@ -12,6 +12,7 @@ from zoneinfo import ZoneInfo
 from app.config import settings
 from app.database import SessionLocal
 from app.services.pipeline import run_pipeline
+from app.services.crawler import refresh_upvotes
 from app.utils import today_str
 
 logger = logging.getLogger(__name__)
@@ -66,6 +67,22 @@ def start_scheduler() -> AsyncIOScheduler | None:
         misfire_grace_time=3600,  # 允许迟到 1 小时内补执行
     )
 
+    # upvote 刷新：每天流水线之后 30 分钟执行，刷新最近 7 天论文的投票数
+    upvote_trigger = CronTrigger(
+        hour=settings.SCHEDULE_HOUR,
+        minute=settings.SCHEDULE_MINUTE + 30,
+        timezone=tz,
+    )
+    scheduler.add_job(
+        _upvote_refresh,
+        trigger=upvote_trigger,
+        id="upvote_refresh",
+        name="upvote_refresh",
+        replace_existing=True,
+        max_instances=1,
+        misfire_grace_time=3600,
+    )
+
     scheduler.start()
     _scheduler = scheduler
     logger.info(
@@ -102,3 +119,19 @@ async def _daily_pipeline() -> None:
         logger.exception("Unexpected error in daily pipeline")
     finally:
         db.close()
+
+
+async def _upvote_refresh() -> None:
+    """刷新最近 N 天论文的 upvotes。"""
+    db: Session = SessionLocal()
+    try:
+        result = await refresh_upvotes(db)
+        logger.info(
+            "Upvote refresh completed: status=%s updated=%d",
+            result.get("status"),
+            result.get("updated", 0),
+        )
+    except Exception:
+        logger.exception("Unexpected error in upvote refresh")
+    finally:
+        db.close()