feat(api+app): 对话阶段化、回忆录流水线与客户端会话体验

- DB: segments 用户输入文本（Alembic 0002）
- Chat: 阶段检测/阶段提示/回复限制，编排与访谈/画像 prompts 调整
- Memoir: 忠实度检查 agent，叙事与分类等链路更新
- Core: agent 日志、Alembic 启动、LangChain/日志/配置等
- Story: time_hints；Memory 检索与相关测试
- Expo: 助手头像、会话页与消息拆分、实时会话与文案/i18n
- Docs/scripts/tests: 迁移脚本、LLM JSON/记忆检索文档、新增单测

api/app/tasks/chapter_compose_tasks.py

@@ -31,13 +31,13 @@ def recompose_chapters_for_story(self, story_id: str) -> dict:
                 memoir_repo.compose_chapter_from_story_links_sync(session, cid)
             session.commit()
         logger.info(
-            "recompose_chapters_for_story: story=%s recomposed_chapters=%s",
+            "recompose_chapters_for_story: story={} recomposed_chapters={}",
             story_id,
             ids,
         )
         return {"story_id": story_id, "recomposed_chapter_ids": ids}
     except Exception as exc:
         logger.warning(
-            "recompose_chapters_for_story failed story=%s err=%s", story_id, exc
+            "recompose_chapters_for_story failed story={} err={}", story_id, exc
         )
         raise self.retry(exc=exc) from exc