feat: 初始提交

backend/app/models/system_config.py

@@ -0,0 +1,14 @@
+from sqlalchemy import String, Text
+from sqlalchemy.orm import Mapped, mapped_column
+
+from ..db.base import Base
+
+
+class SystemConfig(Base):
+    """系统级配置项，例如默认 LLM API Key、模型名称等。"""
+
+    __tablename__ = "system_configs"
+
+    key: Mapped[str] = mapped_column(String(100), primary_key=True)
+    value: Mapped[str] = mapped_column(Text, nullable=False)
+    description: Mapped[str | None] = mapped_column(String(255))