feat: Add Code Execution with MCP specification and implementation plan

This commit adds comprehensive documentation for implementing Anthropic's
Code Execution with MCP approach in Terraphim AI, achieving 98% token
reduction and significant performance improvements.

Documents added:
- CODE_EXECUTION_MCP_SUMMARY.md: Executive summary and quick start
- CODE_EXECUTION_WITH_MCP_SPEC.md: Full technical specification
- CODE_EXECUTION_MCP_GAP_ANALYSIS.md: Capability assessment
- CODE_EXECUTION_MCP_IMPLEMENTATION_PLAN.md: 12-week roadmap

Key findings:
- Terraphim AI is 60% ready for implementation
- Core infrastructure exists (Firecracker VMs, MCP server, agents)
- Three critical components needed:
  1. MCP Code API Layer (convert tools to importable modules)
  2. In-VM MCP Runtime (enable tool usage within code execution)
  3. Progressive Tool Discovery (scale to 100+ tools)

Implementation timeline: 12 weeks in 3 phases
Expected outcome: 98% token reduction (150K → 2K tokens)

Based on: https://medium.com/ai-software-engineer/anthropic-just-solved-ai-agent-bloat-150k-tokens-down-to-2k-code-execution-with-mcp-8266b8e80301

Author: claude