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_list.py

@@ -0,0 +1,70 @@
+import json
+from unittest.mock import AsyncMock, MagicMock
+
+import pytest
+
+from app.core.redis import RedisService
+
+
+@pytest.mark.asyncio
+async def test_add_message_uses_rpush_pipeline() -> None:
+    service = RedisService()
+    client = AsyncMock()
+    pipe = MagicMock()
+    pipe.execute = AsyncMock(return_value=[])
+    client.pipeline = MagicMock(return_value=pipe)
+    service._client = client
+
+    ok = await service.add_message("conv-1", "user", "hello")
+
+    assert ok is True
+    pipe.rpush.assert_called_once()
+    pipe.expire.assert_called_once_with(
+        "conversation:history:conv-1", service.session_ttl
+    )
+    pipe.execute.assert_awaited_once()
+    client.get.assert_not_called()
+
+
+@pytest.mark.asyncio
+async def test_get_conversation_history_migrates_legacy_string() -> None:
+    service = RedisService()
+    client = AsyncMock()
+    legacy = [{"role": "user", "content": "hi", "messageType": "text"}]
+    client.exists.return_value = 1
+    client.type.return_value = "string"
+    client.get.return_value = json.dumps(legacy, ensure_ascii=False)
+    pipe = MagicMock()
+    pipe.execute = AsyncMock(return_value=[])
+    client.pipeline = MagicMock(return_value=pipe)
+    service._client = client
+
+    history = await service.get_conversation_history("conv-legacy")
+
+    assert history == legacy
+    pipe.execute.assert_awaited_once()
+
+
+@pytest.mark.asyncio
+async def test_append_tts_updates_list_entry() -> None:
+    service = RedisService()
+    client = AsyncMock()
+    item = {
+        "role": "ai",
+        "content": "reply",
+        "messageType": "text",
+        "timestamp": "2026-01-01T00:00:00+00:00",
+    }
+    client.exists.return_value = 1
+    client.type.return_value = "list"
+    client.lrange.return_value = [json.dumps(item, ensure_ascii=False)]
+    service._client = client
+
+    ok = await service.append_tts_audio_url_to_last_ai_message(
+        "conv-1", "https://cdn.example/audio.mp3"
+    )
+
+    assert ok is True
+    client.lset.assert_awaited_once()
+    updated = json.loads(client.lset.await_args.args[2])
+    assert updated["ttsAudioUrls"] == ["https://cdn.example/audio.mp3"]