feat: add board group models and update related interfaces

backend/app/models/board_groups.py

@@ -0,0 +1,20 @@
+from __future__ import annotations
+
+from datetime import datetime
+from uuid import UUID, uuid4
+
+from sqlmodel import Field
+
+from app.core.time import utcnow
+from app.models.tenancy import TenantScoped
+
+
+class BoardGroup(TenantScoped, table=True):
+    __tablename__ = "board_groups"
+
+    id: UUID = Field(default_factory=uuid4, primary_key=True)
+    name: str
+    slug: str = Field(index=True)
+    description: str | None = None
+    created_at: datetime = Field(default_factory=utcnow)
+    updated_at: datetime = Field(default_factory=utcnow)