feat(13-02): add device_interfaces table migration and ORM model

- Migration 032 creates device_interfaces with RLS, MAC index, unique(device_id, name)
- DeviceInterface SQLAlchemy model with all columns and device relationship

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/models/device_interface.py

@@ -0,0 +1,49 @@
+"""DeviceInterface model -- interface metadata for MAC-to-device resolution."""
+
+import uuid
+from datetime import datetime
+
+from sqlalchemy import Boolean, DateTime, ForeignKey, String, UniqueConstraint, func
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.models.base import Base
+
+
+class DeviceInterface(Base):
+    __tablename__ = "device_interfaces"
+    __table_args__ = (
+        UniqueConstraint("device_id", "name", name="uq_device_interfaces_device_name"),
+    )
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        primary_key=True,
+        default=uuid.uuid4,
+        server_default=func.gen_random_uuid(),
+    )
+    device_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("devices.id", ondelete="CASCADE"),
+        nullable=False,
+        index=True,
+    )
+    tenant_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("tenants.id", ondelete="CASCADE"),
+        nullable=False,
+        index=True,
+    )
+    name: Mapped[str] = mapped_column(String(255), nullable=False)
+    mac_address: Mapped[str] = mapped_column(String(17), nullable=False)
+    type: Mapped[str] = mapped_column(String(50), nullable=False)
+    running: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False)
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now(), nullable=False
+    )
+
+    # Relationships
+    device: Mapped["Device"] = relationship("Device")  # type: ignore[name-defined]
+
+    def __repr__(self) -> str:
+        return f"<DeviceInterface id={self.id} name={self.name!r} mac={self.mac_address!r}>"