Fix/application ready polish

[savbcar]

**## Summary

• fixes invalid GitHub Actions YAML
• restores Markdown rendering in project documentation
• adds coefficient-of-variation support required by the stochastic study
• adds regression coverage for stochastic reporting
• aligns material-domain validation with the configuration contract
• replaces the README with a recruiter-facing engineering project showcase

Verification

• Ruff formatting check
• Ruff lint
• mypy strict type check
• pytest
• representative engineering workflows
• documentation reviewed**