feat(up): capture follower snapshots at ingest and backfill history

tests/test_repository.py

@@ -339,9 +339,17 @@ def test_up_follower_snapshot_and_backfill():
             assert repo.get_video(3)["up_follower"] == 88
             assert repo.get_video(3)["up_follower_backfilled"] == 1
 
+            # live_since 之前的视频标为回填，之后的视为实时采集
+            repo.upsert_from_fav(resource(5, up_mid=300), F1.media_id, was_added=True)
+            repo.apply_up_follower(
+                mid=300, name="UP3", follower=50, now=now + 180,
+                live_since=now + 1,
+            )
+            assert repo.get_video(5)["up_follower_backfilled"] == 1
+
             coverage = repo.up_follower_coverage()
             assert coverage == {
-                "total": 4, "covered": 4, "missing": 0, "ups_covered": 2,
+                "total": 5, "covered": 5, "missing": 0, "ups_covered": 3,
             }
         finally:
             db.close()