fix(docs): transform README to user-focused guide with debugging split

- Replace technical README with user journey approach
- Add visual problem/solution table with before/after examples
- Create 3-step Quick Start focusing on --fix-all use case
- Move verbose debugging details to new docs/troubleshooting.md
- Fix ASCII tree diagram alignment for depth visualization
- Switch from static to dynamic GitHub release version badge
- Drop Python 3.7 support (EOL), minimum now 3.8+

This restructuring makes the tool immediately accessible to users
who just want to fix their folder dates, while preserving technical
details in dedicated documentation for those who need them.

Author: djdarcy