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

backend/app/models/organizations.py

@@ -0,0 +1,19 @@
+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 Organization(SQLModel, table=True):
+    __tablename__ = "organizations"
+    __table_args__ = (UniqueConstraint("name", name="uq_organizations_name"),)
+
+    id: UUID = Field(default_factory=uuid4, primary_key=True)
+    name: str = Field(index=True)
+    created_at: datetime = Field(default_factory=utcnow)
+    updated_at: datetime = Field(default_factory=utcnow)