feat(classify): gate loose re token, non-linear negatives, drop 纯享/转场

reaction 词表用 re|reaction|反应 但须与咻咻满或充电同现，兼容 reactio/reation 等拼写又避免通用词加分；负向改为每词 -2 且命中多条额外叠加（k*(k-1)），日期 -4；纯享（误伤纯享受）移出负向，转场移出正向。库内 796 条有效视频复测：线以下由 14 降至 8。

tests/test_discovery.py

@@ -128,10 +128,10 @@ def test_filters_and_scoring():
             assert summary.title_miss == 1
             assert summary.old == 1
             assert summary.blacklisted == 1
-            assert summary.candidates == 1  # aid 6
+            assert summary.candidates == 2  # aid 6（1 分）与 aid 2（2 分）
             assert summary.notified == 0
             assert repo.get_candidate(6)["score"] == 1
-            assert repo.get_candidate(2) is None
+            assert repo.get_candidate(2)["score"] == 2  # reaction 命中后单个「切片」不再清零
             assert repo.get_candidate(4) is None
             assert repo.get_candidate(5) is None
             assert notifier.batches == []