feat: explain activity data quality

apps/api/tests/test_activity.py

@@ -86,7 +86,17 @@ def test_repeated_reports_from_one_player_do_not_add_unique_player_weight(db: Se
 
     assert row.catches == 3
     assert row.unique_players == 1
-    assert "3 свежих уловов от 1 игроков" in row.explanation
+    assert "3 свежих улова от 1 игрока" in row.explanation
+
+
+def test_explanation_describes_low_data_and_confidence(db: Session) -> None:
+    add_report(db, age_hours=2, player="Player", confidence=50)
+
+    row = activity_rows(db, hours=6, now=NOW)[0]
+
+    assert row.explanation.startswith("Низкая активность: 1 свежий улов от 1 игрока.")
+    assert "Уверенность низкая." in row.explanation
+    assert "Данных мало: нужно хотя бы 3 наблюдения." in row.explanation
 
 
 def test_pending_rejected_and_deleted_reports_are_excluded(db: Session) -> None: