feat: implement pivot-currency model, rbac smart tokens & fix circular imports

backend/app/models/system.py

@@ -0,0 +1,13 @@
+from sqlalchemy import Column, String, JSON, DateTime, Boolean
+from sqlalchemy.sql import func
+from app.db.base_class import Base
+
+class SystemParameter(Base):
+    __tablename__ = "system_parameters"
+    __table_args__ = {"schema": "data", "extend_existing": True}
+
+    key = Column(String, primary_key=True, index=True, nullable=False)
+    value = Column(JSON, nullable=False)
+    is_active = Column(Boolean, default=True)
+    description = Column(String)
+    updated_at = Column(DateTime(timezone=True), onupdate=func.now(), server_default=func.now())