* docs: rename brownfield to established projects
Flatten how-to/brownfield/ subdirectory and replace jargon term
"brownfield" with more accessible "established projects" throughout.
- brownfield/index.md → established-projects.md
- brownfield/quick-fix-in-brownfield.md → quick-fixes.md
- brownfield-faq.md → established-projects-faq.md
- Update all internal links and references
* docs: remove redundant phrase from quick-fixes description
* docs: restore natural language in established-projects body
Alex Verkhovsky