feat: add organization-related models and update schemas for organization management

backend/app/models/organization_members.py

@@ -0,0 +1,29 @@
+from __future__ import annotations
+
+from datetime import datetime
+from uuid import UUID, uuid4
+
+from sqlalchemy import UniqueConstraint
+from sqlmodel import Field, SQLModel
+
+from app.core.time import utcnow
+
+
+class OrganizationMember(SQLModel, table=True):
+    __tablename__ = "organization_members"
+    __table_args__ = (
+        UniqueConstraint(
+            "organization_id",
+            "user_id",
+            name="uq_organization_members_org_user",
+        ),
+    )
+
+    id: UUID = Field(default_factory=uuid4, primary_key=True)
+    organization_id: UUID = Field(foreign_key="organizations.id", index=True)
+    user_id: UUID = Field(foreign_key="users.id", index=True)
+    role: str = Field(default="member", index=True)
+    all_boards_read: bool = Field(default=False)
+    all_boards_write: bool = Field(default=False)
+    created_at: datetime = Field(default_factory=utcnow)
+    updated_at: datetime = Field(default_factory=utcnow)