[rewrite] Minor fixes to models, session generator and example .env

backend/app/database/models/user_model.py

@@ -26,7 +26,7 @@ class User(SQLModel, table=True):
     owned_shops: List["Shop"] = Relationship(back_populates="owner")
     registered_shop: List["Shop"] = Relationship(back_populates="registered_users")
 
-    role: Optional["UserRole"] = Relationship(back_populates="users")
+    user_assigned_role: Optional["UserRole"] = Relationship(back_populates="role_users", sa_relationship_kwargs={"foreign_keys": "[User.user_role_id]"})
     preferences: Optional["UserPreferences"] = Relationship(back_populates="user")
     statistics: Optional["UserStatistics"] = Relationship(back_populates="user_statistics")
 
@@ -45,7 +45,7 @@ class UserRole(SQLModel, table=True):
     id: int = Field(primary_key=True)
     name: str = Field(nullable=False, unique=True, max_length=50)
 
-    users = Relationship(back_populates="role")
+    role_users: List["User"] = Relationship(back_populates="user_assigned_role")
 
 
 class UserStatistics(SQLModel, table=True):