feat: implement complete CMT backend with API endpoints and test suite

- Add 7 core API endpoints: users, transactions, partners, products, inventory, payments, credit
- Implement role-based authentication (admin/write/read-only access)
- Add comprehensive database models with proper relationships
- Include full test coverage for all endpoints and business logic
- Set up Alembic migrations and Docker configuration
- Configure FastAPI app with CORS and database integration

.copilotignore

@@ -0,0 +1,26 @@
+# Environment files
+.env
+.env.*
+.env.local
+.env.production
+.env.development
+.env.staging
+.env.example
+
+# Security files
+*.key
+*.pem
+*.p12
+*.pfx
+secrets/
+**/*.secret
+**/*.token
+
+# Database files
+*.db
+*.sqlite
+*.sqlite3
+
+# Configuration with sensitive data
+config/database.yml
+config/secrets.yml