feat(projects): add projects app's basic structure and endpoints

apps/projects/services/rates.py

@@ -0,0 +1,42 @@
+from apps.projects.models import ProjectRate, ProjectUserRate
+
+def create_project_rate(project, amount, currency="USD"):
+    return ProjectRate.objects.create(
+        project=project,
+        amount=amount,
+        currency=currency
+    )
+
+def update_project_rate(rate_instance, **kwargs):
+    update_fields = []
+    for field, value in kwargs.items():
+        if hasattr(rate_instance, field) and getattr(rate_instance, field) != value:
+            setattr(rate_instance, field, value)
+            update_fields.append(field)
+            
+    if update_fields:
+        update_fields.append("updated_at")
+        rate_instance.save(update_fields=update_fields)
+        
+    return rate_instance
+
+def create_project_user_rate(project, user, amount, currency="USD"):
+    return ProjectUserRate.objects.create(
+        project=project,
+        user=user,
+        amount=amount,
+        currency=currency
+    )
+
+def update_project_user_rate(user_rate_instance, **kwargs):
+    update_fields = []
+    for field, value in kwargs.items():
+        if hasattr(user_rate_instance, field) and getattr(user_rate_instance, field) != value:
+            setattr(user_rate_instance, field, value)
+            update_fields.append(field)
+            
+    if update_fields:
+        update_fields.append("updated_at")
+        user_rate_instance.save(update_fields=update_fields)
+        
+    return user_rate_instance