feat(Worker): add initial web worker implementation for background processing

- Introduces Target/Worker.js (2610 bytes) to handle computationally intensive tasks in a background thread
- Aligns with Land's performance optimization goals by preventing UI blocking during extension host operations
- Establishes foundation for offloading VS Code extension execution or resource-heavy editor features from main process
- Enables future parallel processing capabilities while maintaining Sky frontend responsiveness
- Implements basic message passing structure for communication between main thread and worker

Author: NikolaRHristov