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/features/memoir/helpers.py

@@ -59,14 +59,14 @@ def normalize_image_assets_for_api(images: list[dict] | None) -> list[dict]:
                 asset["url"] = storage.get_download_url(storage_key)
             except CosDownloadUrlError as exc:
                 logger.warning(
-                    "章节图片签名失败: key=%s, retryable=%s, error=%s",
+                    "章节图片签名失败: key={}, retryable={}, error={}",
                     storage_key,
                     exc.retryable,
                     exc,
                 )
                 asset = mark_image_delivery_unavailable(asset)
             except Exception as exc:
-                logger.warning("章节图片签名失败: key=%s, error=%s", storage_key, exc)
+                logger.warning("章节图片签名失败: key={}, error={}", storage_key, exc)
                 asset = mark_image_delivery_unavailable(asset)
         else:
             asset["url"] = normalized_url