docs: streamline P3 audit documentation to essential high-signal content

- Create 3 core documents addressing auditor's specific requests:
  * CODE_EVOLUTION.md: Code provenance (30% forked, 20% Velodrome, 50% original)
  * MATH_AND_DESIGN.md: Mathematical formulas with implementation references
  * SECURITY_CONSIDERATIONS.md: Critical upgrade safety mechanisms

- Update AUDIT_SCOPE_P3.md to complement (not duplicate) technical docs
- Streamline AUDIT_SUMMARY.md to focus only on essential documents
- Add Mermaid diagrams throughout for better visualization
- Properly credit Velodrome for permanent staking innovation
- Remove low-signal files and redundant documentation

This focused approach directly addresses the two auditor requests:
1. Mathematical formulas underlying StakeWeight.sol
2. Clear attribution of forked vs original code

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

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

Author: rplusq