Add evaluation harness and quality regression guardrails

[NayanKanaparthi]

Context

Tokenomics reliably measures cost and latency, but quality evaluation
is currently heuristic and informal.

As routing and compression strategies evolve, we need a way to ensure
optimizations do not silently degrade output quality.

Open problem

• Define repeatable evaluation benchmarks
• Introduce quality scoring or acceptance thresholds
• Add regression tests that fail when quality drops beyond tolerance

Notes

This does not require perfect "ground truth" quality metrics —
even coarse guardrails would be a meaningful improvement.