docs: clean up redundant and duplicate documentation

Comprehensive cleanup of duplicate and redundant documentation files:

Removed duplicates:
- Deleted .github/workflows-backup/ directory (outdated backup)
- Removed docs/CORS-SECURITY-CONFIGURATION.md (kept comprehensive guide version)
- Consolidated xApp SDK docs (kept development guide, removed architectural version)
- Moved test reports from root to appropriate directories

Canonical versions preserved:
- docs/CORS-Security-Configuration-Guide.md (comprehensive version)
- docs/xApp-Development-SDK-Guide.md (complete development guide)
- docs/adr/ADR-006-adoption-of-go-1.24.md (renumbered from ADR-001)
- tests/comprehensive-test-summary-report.md (moved from root)
- docs/security/ (consolidated security implementation docs)

Updated references:
- Fixed workflows-backup references in cleanup documentation
- Updated cross-references to moved files
- Maintained single canonical version for each document type

This cleanup eliminates documentation duplication, improves organization,
and ensures a single source of truth for all project documentation.

Author: thc1006