feat: add device_types table with system seed data

Creates DeviceType SQLAlchemy model and migration 073 that provisions the
device_types table with 28 system-seeded device types across 7 categories
(network, compute, storage, cloud, endpoint, infrastructure, security).

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

backend/app/models/__init__.py

@@ -54,6 +54,7 @@ from .session_branch import SessionBranch
 from .fork_point import ForkPoint
 from .session_handoff import SessionHandoff
 from .session_resolution_output import SessionResolutionOutput
+from .device_type import DeviceType
 
 __all__ = [
     "User",
@@ -122,4 +123,5 @@ __all__ = [
     "ForkPoint",
     "SessionHandoff",
     "SessionResolutionOutput",
+    "DeviceType",
 ]

backend/app/models/device_type.py

@@ -0,0 +1,51 @@
+"""Device type model for network diagrams."""
+import uuid
+from datetime import datetime, timezone
+from typing import Optional, TYPE_CHECKING
+
+from sqlalchemy import String, Boolean, Integer, DateTime, ForeignKey
+from sqlalchemy.orm import Mapped, mapped_column
+from sqlalchemy.dialects.postgresql import UUID
+
+from app.core.database import Base
+
+if TYPE_CHECKING:
+    pass
+
+
+class DeviceType(Base):
+    """A device type for network diagram nodes (system or team-custom)."""
+    __tablename__ = "device_types"
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), primary_key=True, default=uuid.uuid4
+    )
+    slug: Mapped[str] = mapped_column(
+        String(50), nullable=False,
+        comment="Unique identifier used in diagram node data",
+    )
+    label: Mapped[str] = mapped_column(
+        String(100), nullable=False,
+        comment="Display name",
+    )
+    category: Mapped[str] = mapped_column(
+        String(50), nullable=False,
+        comment="network, compute, storage, cloud, endpoint, infrastructure, security",
+    )
+    is_system: Mapped[bool] = mapped_column(
+        Boolean, nullable=False, default=False,
+        comment="True for built-in types that cannot be deleted",
+    )
+    team_id: Mapped[Optional[uuid.UUID]] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("teams.id", ondelete="CASCADE"),
+        nullable=True,
+        comment="NULL for system types, set for team-custom types",
+    )
+    sort_order: Mapped[int] = mapped_column(
+        Integer, nullable=False, default=0,
+        comment="Display order within category",
+    )
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
+    )