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/story_route_agent.py

@@ -21,6 +21,8 @@ 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.story.models import Story
+from app.features.memoir.constants import memoir
+from app.features.story.constants import story
 
 logger = get_logger(__name__)
 
@@ -47,7 +49,7 @@ def default_append_target_story_id(
     ordered = sort_stories_for_route(
         candidate_stories,
         meta,
-        summary_min_chars=int(settings.story_route_summary_min_chars),
+        summary_min_chars=int(story.route_summary_min_chars),
     )
     if not ordered:
         return None
@@ -247,7 +249,7 @@ class StoryRouteAgent:
             llm,
             prompt,
             StoryRouteDecision,
-            max_tokens=settings.memoir_story_route_max_tokens,
+            max_tokens=memoir.story_route_max_tokens,
             agent="StoryRouteAgent.decide",
             fallback_factory=_decide_fallback,
         )
@@ -295,7 +297,7 @@ class StoryRouteAgent:
                 llm,
                 prompt,
                 StoryBatchPlan,
-                max_tokens=settings.memoir_story_batch_plan_max_tokens,
+                max_tokens=memoir.story_batch_plan_max_tokens,
                 agent="StoryRouteAgent.plan_batch",
             )
         except LLMCallError as e: