refactor(tm-core): migrate to Vitest and Biome, implement clean architecture

- Migrated from Jest to Vitest for faster test execution (~4.2s vs ~4.6-5s)
- Replaced ESLint and Prettier with Biome for unified, faster linting/formatting
- Implemented BaseProvider with Template Method pattern following clean code principles
- Created TaskEntity with business logic encapsulation
- Added TaskMasterCore facade as main entry point
- Implemented complete end-to-end listTasks functionality
- All 50 tests passing with improved performance

🤖 Generated with Claude Code

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

packages/tm-core/src/index.ts

@@ -3,6 +3,14 @@
  * This file exports all public APIs from the core Task Master library
  */
 
+// Export main facade
+export {
+	TaskMasterCore,
+	createTaskMasterCore,
+	type TaskMasterCoreOptions,
+	type ListTasksResult
+} from './task-master-core.js';
+
 // Re-export types
 export type * from './types/index';
 
@@ -25,6 +33,9 @@ export * from './utils/index';
 // Re-export errors
 export * from './errors/index';
 
+// Re-export entities
+export { TaskEntity } from './core/entities/task.entity.js';
+
 // Package metadata
 export const version = '1.0.0';
 export const name = '@task-master/tm-core';