feat: Refactor user context handling and service methods

- Updated middleware to fetch user and tenant models by ID and set them in context.
- Refactored common service methods to accept userID as a parameter instead of extracting from context.
- Modified content service methods to include userID as a parameter for better clarity and performance.
- Adjusted coupon, creator, notification, order, tenant, user, and wallet services to utilize userID directly.
- Enhanced context key constants for improved readability and maintainability.

backend/pkg/consts/context_keys.go

@@ -1,8 +1,8 @@
 package consts
 
 const (
-	CtxKeyTenant     = "tenant"
-	CtxKeyClaims     = "claims"
-	CtxKeyUser       = "user"
-	CtxKeyTenantUser = "tenant_user"
+	CtxKeyTenant     = "__ctx_tenant"
+	CtxKeyClaims     = "__ctx_claims"
+	CtxKeyUser       = "__ctx_user"
+	CtxKeyTenantUser = "__ctx_tenant_user"
 )