Coverage-guided scheduling: prioritize mutants by response clusters they reach

[cy3erm]

From the roadmap.

Track which response clusters new mutants reach and prioritize unexplored regions, AFL-style. The pieces already exist:

• responses are fingerprinted and clustered (protoforge/fuzz/classify.py, analysis/clustering.py)
• the scheduler is a simple rate limiter today (protoforge/fuzz/scheduler.py)

Goal: an interestingness signal per cluster that biases case ordering within a run, while keeping seed determinism.