Extends match-pattern in spec/evaluator.sx with an ADT case: when the
pattern is (CtorName var...) and the value is an ADT dict (:_adt true),
check :_ctor matches, arity matches, then recursively bind field patterns.
Supports nested patterns, wildcard _, variable binding, and zero-arg ctors.
Changes step-sf-match to route no-clause errors through raise-eval-frame
instead of direct error, allowing guard to catch non-exhaustive matches.
40/40 ADT tests pass (20 define-type + 20 match). Zero regressions.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
giles
0dc7e1599c