POL-7: Add disciplines table

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/models/discipline.py

@@ -0,0 +1,20 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import DateTime, ForeignKey, JSON, String, Uuid, func
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.database import Base
+
+
+class Discipline(Base):
+    __tablename__ = "disciplines"
+
+    id: Mapped[uuid.UUID] = mapped_column(Uuid(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    championship_id: Mapped[uuid.UUID] = mapped_column(Uuid(as_uuid=True), ForeignKey("championships.id", ondelete="CASCADE"), nullable=False)
+    name: Mapped[str] = mapped_column(String(255), nullable=False)
+    levels: Mapped[list | None] = mapped_column(JSON)  # e.g. ["Amateur", "Pro", "Open"]
+
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())
+
+    championship: Mapped["Championship"] = relationship(back_populates="disciplines")  # type: ignore[name-defined]