新增PDF生成并发设置

backend/app/schemas/setting.py

@@ -0,0 +1,12 @@
+from datetime import datetime
+
+from pydantic import BaseModel, Field
+
+
+class PdfSettingsOut(BaseModel):
+    pdf_generation_concurrency_limit: int
+    updated_at: datetime | None = None
+
+
+class PdfSettingsUpdate(BaseModel):
+    pdf_generation_concurrency_limit: int = Field(ge=1, le=10)