docs: improve dynamic routes example in project structure page (#84086)
## Documentation Update
This PR improves the dynamic routes example in the
`project-structure.mdx` page.
### Changes
- Updated catch-all segments example:
- Before: `/shop/clothing/shoes`
- After: `/shop/clothing`
- Adjusted follow-up examples for consistency:
- `/shop/a`, `/shop/a/b` → `/shop/clothing`, `/shop/clothing/shirts`
### Why
- Provides a clearer and more intuitive demonstration of how catch-all
segments work.
- Keeps the example consistent with other dynamic routes documentation.
Co-authored-by: Joseph <joseph.chamochumbi@vercel.com>