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

backend/app/models/system_config.py

@@ -0,0 +1,16 @@
+from sqlalchemy import Column, String, JSON, Integer, Boolean, DateTime, func
+from app.db.base_class import Base
+
+class SystemParameter(Base):
+    """
+    Globális rendszerbeállítások (A meglévő data.system_parameters tábla alapján).
+    """
+    __tablename__ = "system_parameters"
+    __table_args__ = {"schema": "data"}
+
+    id = Column(Integer, primary_key=True, index=True)
+    key = Column(String(50), unique=True, index=True, nullable=False)
+    value = Column(JSON, nullable=False)
+    is_active = Column(Boolean, default=True)
+    description = Column(String, nullable=True)
+    updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now())