fix: normalize embedded JSON in text fields for clean diffs

- Enhanced normalizeProbeResult to parse and re-normalize JSON strings
  found in 'text' fields (common in tool call responses)
- Matches jq -S behavior from github-mcp-server reference implementation
- Added comprehensive test coverage for normalizeProbeResult

Fixes diff churn caused by key ordering inconsistencies in embedded JSON.

Author: SamMorrowDrums