Add unit tests for player configurations and referral system

- Implement tests for player configuration creation, update, and deletion, ensuring proper handling of free and paid user scenarios.
- Add tests for referral registration, including valid and invalid referrer cases.
- Create tests for referral reward flow, verifying correct reward distribution and eligibility.
- Establish a test database setup with necessary schema for user, plan, payment, and notification models.
- Introduce helper functions for seeding test data and loading entities from the database.

.gitignore

@@ -30,6 +30,5 @@ go.work.sum
 # OS-specific junk
 .DS_Store
 Thumbs.db
-server
 # Module cache (if you're using GOPATH, which is rare now)
 Godeps/