feat(backend): add database models

backend/src/models/base.py

@@ -0,0 +1,38 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import DateTime, func
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column
+
+
+class Base(DeclarativeBase):
+    """Base class for all models."""
+
+    pass
+
+
+class TimestampMixin:
+    """Mixin that adds created_at and updated_at timestamps."""
+
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        server_default=func.now(),
+        nullable=False,
+    )
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        server_default=func.now(),
+        onupdate=func.now(),
+        nullable=False,
+    )
+
+
+class UUIDMixin:
+    """Mixin that adds a UUID primary key."""
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        primary_key=True,
+        default=uuid.uuid4,
+    )