refactor(api): TOML 配置 SSOT、统一错误契约、Auth/事务加固与可观测性 (#33)

配置 SSOT（TOML + .env）
统一错误契约
Auth 与事务边界
Redis / Celery 可靠性:业务 Redis（DB/0）与 Celery broker/backend（DB/1）显式拆分；连接池、sync client
可观测性（OpenTelemetry + LGTM）

api/tests/test_memoir_skip_story.py

@@ -14,6 +14,7 @@ from app.agents.memoir.extraction_agent import ExtractionResult
 from app.agents.memoir.orchestrator import MemoirOrchestrator
 from app.agents.stage_constants import CHAT_STAGES
 from app.agents.state_schema import DEFAULT_STAGE_ORDER, MemoirStateSchema
+from app.features.memoir.constants import memoir
 
 
 def _empty_state() -> MemoirStateSchema:
@@ -123,7 +124,7 @@ def test_prepare_batches_batch_llm_path_matches_per_segment_skip_logic(
     monkeypatch: pytest.MonkeyPatch,
 ) -> None:
     monkeypatch.setattr(
-        "app.agents.memoir.orchestrator.settings.memoir_phase1_batch_llm_enabled",
+        "app.agents.memoir.orchestrator.memoir.phase1_batch_llm_enabled",
         True,
     )