[US-017] Documentation - Complete README

[quotentiroler]

Story

Write comprehensive documentation.

Acceptance Criteria

• Update README.md with: project vision (physical energy concept), the 3-gate model explanation, quick start guide, API reference, CLI reference, Ralph integration guide, metric definitions (PoE-LOC, Verified LOC, Ralph), AI Explorer guide, contributing guide for benchmark PRDs
• Include architecture diagram reference to image.png
• Add CONTRIBUTING.md with benchmark PRD submission guidelines
• Typecheck passes (for any code examples)

Context

• Read AGENTS.md for project context
• Read ARCHITECTURE.md for code patterns
• Depends on: All previous stories for accurate documentation

Notes

Documentation makes the project usable and the concepts clear.