fix(P0-03): Prediction 幂等指纹——只追加,不覆盖

_upsert_prediction 改为 _insert_or_find_by_fingerprint:
- 同 input_hash → 返回已有行(绝不 UPDATE pred_/reasoning/agent_outputs)
- 不同 input_hash → INSERT 新行

input_hash 升级为规范 JSON SHA-256,捕获:match_id, cutoff, prompt_version,
prompt_hash, system_prompt_hash, provider, model, mode, run_type, temperature,
context_hash, agent_ids。移除旧 (match, provider, model, mode, run_type) 唯一约束,
改为 partial unique index(WHERE input_hash IS NOT NULL,兼容旧 NULL 数据)。

三条路径(single/multi/baseline)统一传足指纹字段。
迁移 0024 + 测试 test_p0_prediction_fingerprint(10/10);全量 295 通过。

tests/test_baseline.py

@@ -89,7 +89,7 @@ async def test_predict_baseline_no_llm():
     with patch("src.llm.baseline._avg_goals", fake_avg), \
          patch("src.llm.baseline.AsyncSessionLocal") as SLC, \
          patch("src.db.unit_of_work.get_uow", _FakeUoW), \
-         patch("src.llm.baseline._upsert_prediction", _fake_upsert):
+         patch("src.llm.baseline._insert_or_find_by_fingerprint", _fake_upsert):
         class FakeSession:
             async def get(self, cls, mid):
                 return FakeMatch()
@@ -137,7 +137,7 @@ async def test_predict_baseline_clamps_to_range():
     with patch("src.llm.baseline._avg_goals", fake_avg), \
          patch("src.llm.baseline.AsyncSessionLocal") as SLC, \
          patch("src.db.unit_of_work.get_uow", _FakeUoW), \
-         patch("src.llm.baseline._upsert_prediction", _fake_upsert):
+         patch("src.llm.baseline._insert_or_find_by_fingerprint", _fake_upsert):
         class FakeSession:
             async def get(self, cls, mid):
                 return FakeMatch()