Name the escape path under the level rule, and date 0.1.1

[pedro-pscunha]

One sentence in docs/contract.md, approved during #6's review and missed by the merge by
about thirty seconds.

main today says a counterexample on a level is refused outright, and that the guarantee is
over declared parts. Both true. What it does not say is where each SDK refuses, or which
path escapes — and the escape path is real: score_levels takes an already-rendered string,
so a rubric carrying a counterexample can be pre-rendered and handed to a level, and
Rubric::render cannot prevent it because it has no idea the string is bound for a level.

That residual was written on the Rust type's doc comment and never reached the contract, which
is the point: a type's doc comment is not what another language's implementer reads. A third
SDK working from main right now has to rediscover the boundary for itself.

It also carries the release prep that cannot go in any other way: main takes pull requests
only, so the CHANGELOG.md heading cannot be dated by a direct push at release time. ## Unreleased becomes ## 0.1.1 (2026-09-22) — the 22nd, not the 21st the first draft carried,
which is why the notes were moved back under Unreleased in the first place.

 CHANGELOG.md     | 2 +-
 docs/contract.md | 9 ++++++---
 2 files changed, 7 insertions(+), 4 deletions(-)

Docs only. No code, no spec/, so nothing for Python to re-vendor. After this merges the
remaining release steps are the tag, cargo publish --workspace --locked, and the GitHub
release.