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/app/agents/memoir/extraction_agent.py

@@ -14,6 +14,7 @@ from app.agents.stage_constants import normalize_chat_stage
 from app.core.config import settings
 from app.core.llm_call import LLMCallError, llm_json_call
 from app.core.logging import get_logger
+from app.features.memoir.constants import memoir
 
 logger = get_logger(__name__)
 
@@ -64,7 +65,7 @@ class ExtractionAgent:
                 llm,
                 prompt,
                 StateExtractionOutput,
-                max_tokens=settings.memoir_extraction_max_tokens,
+                max_tokens=memoir.extraction_max_tokens,
                 agent="ExtractionAgent.extract",
             )
             raw_slots = parsed.slots or {}