Support SQLAlchemy polymorphic / table inheritance

[JoseVelazcoH]

Problem

SQLAlchemy supports single-table, joined-table, and concrete-table inheritance via __mapper_args__. These patterns are very common in real applications but are currently not visualized — inheritance relationships are either ignored or shown as plain FK arrows with no distinction.

Example

class Employee(Base):
    __tablename__ = "employee"
    __mapper_args__ = {"polymorphic_on": type, "polymorphic_identity": "employee"}

class Manager(Employee):
    __tablename__ = "manager"
    __mapper_args__ = {"polymorphic_identity": "manager"}

Expected

Inheritance edges should be rendered differently from FK edges (e.g. a hollow arrow or dashed line) and labeled with the inheritance strategy (joined / single / concrete).