docs(represent): close LOOP-1 and define PARETO-1's value-sensitive gate

[chrishayuk]

REPRESENT-LOOP-1 is complete: A (#474), B (#475), and the paired C witness (#476) are reviewed and merged. This records C's merge at 23a56db1, after every workflow passed on ac892f2e, including both mutation jobs.

The next proposed experimental milestone is REPRESENT-PARETO-1: accepted quality values and grounded physical costs must change measured-candidate preference. Its primary control holds candidate keys, observed-key sets, cost facts and policy fixed across independent counterfactual replays, so AlreadyObserved cannot explain the result. It also requires a physical-cost control, replay determinism, transactional rejection and preservation of ambiguity when evidence cannot justify a winner.

The first-gate assumption is a tiny controlled fixture before real numerical measurements. Concrete numeric inputs, cost provenance and expected decisions must be frozen before implementation. This PR registers the claim and controls; it does not claim a PARETO result or implement a new policy.

The existing boundary is explicit: PhysicalPrizeFirst orders unmeasured experiments, while accepted quality values feed the measured-preference path. Generalizing to unseen neighbours and installing a promoted incumbent are separate claims. Existing K3 authority debts remain recorded.

Validation: all milestone JSON parses; 105 contract witnesses, 867 relative documentation links and 1,448 strict references pass; git diff --check passes. Documentation only.

Completed milestone · PARETO-1 design