feat(server): 更新用户代理服务架构，增强用户行为追踪和会话管理功能，包含schema、service和单元测试

server/src/app/schemas/user_agent.py

@@ -117,6 +117,8 @@ class UserAgentReviewDocumentCard(BaseModel):
     scene_label: str = Field(default="", description="面向用户展示的场景标签。")
     summary: str = Field(default="", description="逐票据摘要。")
     avg_score: float = Field(default=0.0, ge=0.0, le=1.0, description="OCR 平均得分。")
+    preview_kind: str = Field(default="", description="票据预览类型，例如 image。")
+    preview_data_url: str = Field(default="", description="票据预览图片 data URL。")
     warnings: list[str] = Field(default_factory=list, description="该票据的识别提示。")
     fields: list[UserAgentReviewDocumentField] = Field(
         default_factory=list,