feat: add board goals, memory, approvals, onboarding models

backend/app/models/board_onboarding.py

@@ -0,0 +1,20 @@
+from __future__ import annotations
+
+from datetime import datetime
+from uuid import UUID, uuid4
+
+from sqlalchemy import JSON, Column
+from sqlmodel import Field, SQLModel
+
+
+class BoardOnboardingSession(SQLModel, table=True):
+    __tablename__ = "board_onboarding_sessions"
+
+    id: UUID = Field(default_factory=uuid4, primary_key=True)
+    board_id: UUID = Field(foreign_key="boards.id", index=True)
+    session_key: str
+    status: str = Field(default="active", index=True)
+    messages: list[dict[str, object]] | None = Field(default=None, sa_column=Column(JSON))
+    draft_goal: dict[str, object] | None = Field(default=None, sa_column=Column(JSON))
+    created_at: datetime = Field(default_factory=datetime.utcnow)
+    updated_at: datetime = Field(default_factory=datetime.utcnow)