chore: remove backup files from refactoring

Cleanup after catalog migration:
- install_core.sh.old (46KB - original 1150 lines)
- install_core.sh.old2 (2.8KB - intermediate version)
- install_core.sh.obsolete (1.4KB - moved to obsolete)
- guide.sh.old (28KB - 664 lines with hard-coded arrays)
- README.md.old (18KB - pre-catalog documentation)

All functionality now in:
- install_tool.sh (orchestrator)
- install_group.sh (tag-based installer)
- guide.sh (171 lines, catalog-driven)
- catalog/*.json (65 tool entries)

Author: AI Assistant