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_conversation_history_turn_ids.py

@@ -2,7 +2,8 @@
 
 from __future__ import annotations
 
-from unittest.mock import AsyncMock, MagicMock
+from contextlib import asynccontextmanager
+from unittest.mock import AsyncMock, MagicMock, patch
 
 import pytest
 from sqlalchemy.ext.asyncio import AsyncSession
@@ -10,8 +11,14 @@ from sqlalchemy.ext.asyncio import AsyncSession
 from app.features.conversation.history_store import HumanAiTurnIds
 
 
+@asynccontextmanager
+async def _capture_transactional(db):
+    yield db
+    await db.commit()
+
+
 @pytest.mark.asyncio
-async def test_record_human_ai_turn_returns_both_message_ids(monkeypatch) -> None:
+async def test_record_human_ai_turn_returns_both_message_ids() -> None:
     conv_id = "conv-1"
     captured: list[object] = []
 
@@ -25,20 +32,19 @@ async def test_record_human_ai_turn_returns_both_message_ids(monkeypatch) -> Non
         def add_conversation_message(msg: object, db) -> None:
             captured.append(msg)
 
-    monkeypatch.setattr(
-        "app.features.conversation.history_store.ConversationMessage",
-        FakeMsg,
-    )
-
     db = MagicMock(spec=AsyncSession)
     db.commit = AsyncMock()
-    db.refresh = AsyncMock()
 
-    import app.features.conversation.history_store as hs_mod
-
-    orig_repo = hs_mod.repo
-    hs_mod.repo = _FakeRepo  # type: ignore[misc]
-    try:
+    with patch(
+        "app.features.conversation.history_store.transactional",
+        _capture_transactional,
+    ), patch(
+        "app.features.conversation.history_store.ConversationMessage",
+        FakeMsg,
+    ), patch(
+        "app.features.conversation.history_store.repo",
+        _FakeRepo,
+    ):
         from app.features.conversation import history_store as hs
 
         store = hs.ConversationHistoryStore(db)
@@ -57,8 +63,6 @@ async def test_record_human_ai_turn_returns_both_message_ids(monkeypatch) -> Non
             segment_id="seg-1",
             memory_retrieval_trace=None,
         )
-    finally:
-        hs_mod.repo = orig_repo  # type: ignore[misc]
 
     assert isinstance(out, HumanAiTurnIds)
     assert len(captured) == 2
@@ -67,3 +71,4 @@ async def test_record_human_ai_turn_returns_both_message_ids(monkeypatch) -> Non
     assert captured[0].segment_id == "seg-1"
     assert out.human_message_id == captured[0].id
     assert out.assistant_message_id == captured[1].id
+    db.commit.assert_awaited_once()