[FEAT] optimise directory structure for easier refactoring

### **Feature**
Optimise directory before refactoring

### **What should be done**
- [x] Apply atomic design system
- [x] Separate codes for the better understandability
- [ ] Remove tailwind

### **Additional context**
Apply atomic design system

Review the repository's current directory structure and the atomic-design organization described in the issue. Locate the remaining Tailwind usage and confirm the intended removal scope; done means Tailwind is removed while the client retains the intended structure. No files or tests are named, so confirm the target entry points and validation steps with maintainers.

Written by the indexing model from the issue text.