feat: bootstrap backend MVP and architecture docs

backend/app/models/user.py

@@ -0,0 +1,23 @@
+from datetime import datetime
+from uuid import uuid4
+
+from sqlalchemy import Boolean, DateTime, String, func
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.db.base import Base
+
+
+class User(Base):
+    __tablename__ = "users"
+
+    id: Mapped[str] = mapped_column(UUID(as_uuid=False), primary_key=True, default=lambda: str(uuid4()))
+    authentik_sub: Mapped[str] = mapped_column(String(255), unique=True, nullable=False, index=True)
+    email: Mapped[str | None] = mapped_column(String(320))
+    display_name: Mapped[str | None] = mapped_column(String(255))
+    is_active: Mapped[bool] = mapped_column(Boolean, default=True, nullable=False)
+
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now(), nullable=False)
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now(), onupdate=func.now(), nullable=False
+    )