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/batch_phase1_prep.py

@@ -15,6 +15,7 @@ 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.conversation.models import Segment
+from app.features.memoir.constants import memoir
 
 logger = get_logger(__name__)
 
@@ -68,7 +69,7 @@ def run_batch_phase1_prep(
             llm,
             prompt,
             BatchPhase1LLMOutput,
-            max_tokens=int(settings.memoir_phase1_batch_llm_max_tokens),
+            max_tokens=int(memoir.phase1_batch_llm_max_tokens),
             agent="BatchPhase1Prep.run",
         )
     except LLMCallError as e: