refactor: reorganize project structure and add comprehensive documentation
- Organize components into subdirectories by type (layout, cards, sections, ui)
- Centralize TypeScript types in src/lib/types/
- Move documentation files to docs/ directory
- Create comprehensive PROJECT_STRUCTURE.md guide
- Add README files for lib/, utils/, tests/, and config/
- Set up test directory structure (unit, integration, e2e)
- Reorganize assets with icons subdirectory
- Fix favicon import path in layout
- Update component exports and imports to reflect new structure
This reorganization improves maintainability, discoverability, and follows
SvelteKit best practices for larger projects.