Fix JIT compile-let shadow binding: evaluate init before defining local

compile-let called scope-define-local eagerly as part of the let
binding, adding the new local to the scope before compile-expr ran
for the init expression. When nested lets rebound the same variable
(e.g. the hyperscript parser's 4 chained `parts` bindings), the init
expression resolved the name to the new uninitialized slot instead of
the outer one — producing nil where it should have read the previous
value.

Move scope-define-local after compile-expr so init expressions see the
outer scope's binding. Fixes all 11 JIT hyperscript parser failures.
3127/3127 JIT + non-JIT, 25/25 standalone hyperscript tests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/compiler.sx

@@ -599,11 +599,12 @@
                 (binding)
                 (let
                   ((name (if (= (type-of (first binding)) "symbol") (symbol-name (first binding)) (first binding)))
-                    (value (nth binding 1))
-                    (slot (scope-define-local let-scope name)))
+                    (value (nth binding 1)))
                   (compile-expr em value let-scope false)
-                  (emit-op em 17)
-                  (emit-byte em slot)))
+                  (let
+                    ((slot (scope-define-local let-scope name)))
+                    (emit-op em 17)
+                    (emit-byte em slot))))
               bindings)
             (compile-begin em body let-scope tail?)))))
     (define