Add comprehensive test suite and update configuration

- Add Jest testing framework configuration
- Add test files for services, types, and utilities
- Update package.json with Jest dependencies and test scripts
- Enhance pre-commit checks to include testing
- Add proper environment validation and error handling in mailgun service

package.json

@@ -16,6 +16,9 @@
     "test": "jest",
     "test:watch": "jest --watch",
     "test:coverage": "jest --coverage",
+    "test:fast": "jest --testPathPatterns='(utils|types|services).*test\\.(ts|js)$' --passWithNoTests",
+    "test:unit": "jest --testPathPatterns='(utils|types).*test\\.(ts|js)$'",
+    "test:services": "jest --testPathPatterns='services.*test\\.(ts|js)$'",
     "test:integration": "jest tests/integration/production.test.js",
     "test:e2e": "playwright test",
     "test:e2e:ui": "playwright test --ui",