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

jest.config.json

@@ -4,6 +4,8 @@
   "setupFilesAfterEnv": ["<rootDir>/tests/setup.ts"],
   "testMatch": [
     "<rootDir>/services/**/__tests__/**/*.test.ts",
+    "<rootDir>/utils/**/__tests__/**/*.test.ts",
+    "<rootDir>/types/**/__tests__/**/*.test.ts",
     "<rootDir>/tests/**/*.test.ts",
     "<rootDir>/tests/**/*.test.js"
   ],
@@ -12,6 +14,7 @@
     "components/**/*.tsx",
     "hooks/**/*.ts",
     "utils/**/*.ts",
+    "types/**/*.ts",
     "!**/*.d.ts",
     "!**/__tests__/**"
   ],