feat(gsm8k): xhigh capability sprint 13 robust lift (#827)
* test(gsm8k): pin xhigh sprint13 confusers and completeness
Add the Sprint 13 contract bundle with target-chain pins, sealed-wrong
neighbors, fraction-word refusals, and non-vacuous completeness cases for
extra mile and extra-actor obligations.
* feat(gsm8k): add xhigh sprint13 verified organs
Gate A2t bounded_rate_projection admits 0016 and 0034 with honest
affine/percent derivations. Gate A2u closed_reference_affine_aggregate
admits 0027 and 0039 with statement-scoped numeric obligations and
repaired comparative provenance. Serving lift: 26/24/0 -> 30/20/0 with
wrong=0 preserved.
* docs(gsm8k): add xhigh sprint13 lookback
Record XHIGH draft recovery, unsafe evidence findings, repairs, Path A
salvage decision, validation outputs, and Sprint 14 recommendation.