feat(backend): added auth, reviews, users modules

also provided tests

src/backend/apps/users/models.py

@@ -1,11 +1,44 @@
 from django.contrib.auth.models import AbstractUser
+from django.db import models
 from django.utils.translation import gettext_lazy as _
 
 from apps.core.models import BaseModel
 
 
+class UserRole(models.TextChoices):
+    ADMIN = "admin", _("Admin")
+    EXPERIMENTER = "experimenter", _("Experimenter")
+    APPROVER = "approver", _("Approver")
+    VIEWER = "viewer", _("Viewer")
+
+
 class User(AbstractUser, BaseModel):
+    role = models.CharField(
+        max_length=20,
+        choices=UserRole.choices,
+        default=UserRole.VIEWER,
+        db_index=True,
+        verbose_name=_("role"),
+        help_text=_("Platform role that defines user permissions"),
+    )
+
     class Meta:
         swappable = "AUTH_USER_MODEL"
         verbose_name = _("user")
         verbose_name_plural = _("users")
+
+    @property
+    def is_admin_role(self) -> bool:
+        return self.role == UserRole.ADMIN
+
+    @property
+    def is_experimenter(self) -> bool:
+        return self.role == UserRole.EXPERIMENTER
+
+    @property
+    def is_approver(self) -> bool:
+        return self.role == UserRole.APPROVER
+
+    @property
+    def is_viewer(self) -> bool:
+        return self.role == UserRole.VIEWER