docs: add comprehensive split brain elimination status report

CRITICAL DOCUMENTATION - 712-line comprehensive analysis:
- Split brain elimination details (metrics + summary)
- Before/after comparisons
- Architectural analysis
- Complete todo list (25 items, prioritized)
- Lessons learned
- Customer value impact
- Technical debt inventory
- Next session roadmap

This is THE definitive record of the split brain elimination work.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: LarsArtmann