feat: add workspace tenant foundations

backend/app/models/workspace.py

@@ -0,0 +1,29 @@
+from datetime import datetime
+
+from sqlalchemy import Boolean, Column, DateTime, Index, Integer, String, Text
+from sqlalchemy.orm import relationship
+
+from app.core.database import Base
+
+
+class Workspace(Base):
+    """Tenant/workspace boundary for monitored DMARC assets."""
+
+    __tablename__ = "workspaces"
+
+    id = Column(Integer, primary_key=True, index=True)
+    slug = Column(String, unique=True, nullable=False, index=True)
+    name = Column(String, nullable=False)
+    description = Column(Text, nullable=True)
+    active = Column(Boolean, default=True, nullable=False, index=True)
+    created_at = Column(DateTime, default=datetime.utcnow, index=True)
+    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
+
+    domains = relationship("Domain", back_populates="workspace")
+    mail_sources = relationship("MailSource", back_populates="workspace")
+    users = relationship("User", back_populates="workspace")
+
+    __table_args__ = (Index("ix_workspaces_active_slug", "active", "slug"),)
+
+    def __repr__(self):
+        return f"<Workspace {self.slug}>"