feat: implement database service with SQL Server and MySQL support

- Add database types (QueryResult, TransactionResult)
- Implement DatabaseService with connection management for SQL Server and MySQL
- Add query execution methods for both database types
- Include comprehensive error handling and logging
- Add unit test for error handling
- Configure Jest for testing

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

jest.config.js

@@ -0,0 +1,8 @@
+module.exports = {
+  preset: 'ts-jest',
+  testEnvironment: 'node',
+  roots: ['<rootDir>/tests'],
+  testMatch: ['**/*.test.ts'],
+  collectCoverageFrom: ['src/**/*.ts', '!src/**/*.d.ts'],
+  moduleFileExtensions: ['ts', 'js', 'json'],
+};