Migrate from master to main branch

- Update GitHub Actions workflow to use main branch
- Update CONTRIBUTING.md to reference main branch
- Align with modern Git and GitHub conventions

Author: cm45t3r

.github/workflows/ci.yml

@@ -2,9 +2,9 @@ name: CI
 
 on:
   push:
-    branches: [ main, master ]
+    branches: [ main ]
   pull_request:
-    branches: [ main, master ]
+    branches: [ main ]
 
 jobs:
   test:

CONTRIBUTING.md

@@ -140,7 +140,7 @@ When reporting bugs or requesting features:
 ## Pull Request Process
 
 1. **Fork the repository**
-2. **Create a feature branch** from `master`
+2. **Create a feature branch** from `main`
 3. **Make your changes**
 4. **Add tests** for new functionality
 5. **Update documentation** if needed