feat: persist photos and enrich conversation history

backend/schemas.py

@@ -467,6 +467,16 @@ class ModelResourceTestResult(CamelModel):
 
 
 # ---------- 对话历史 ----------
+class ConversationArtifactOut(CamelModel):
+    id: str
+    kind: str
+    content_url: str
+    mime_type: str
+    size_bytes: int | None = None
+    duration_ms: int | None = None
+    extra: dict[str, Any] = Field(default_factory=dict)
+
+
 class ConversationMessageOut(CamelModel):
     id: str
     sequence: int
@@ -475,6 +485,7 @@ class ConversationMessageOut(CamelModel):
     content: str
     occurred_at: datetime
     extra: dict[str, Any] = Field(default_factory=dict)
+    artifacts: list[ConversationArtifactOut] = Field(default_factory=list)
 
 
 class ConversationOut(CamelModel):