HS: return/guard, repeat while/until, if-then fix, script extraction

Parser: if-then consumes 'then' keyword before parsing then-body.
Compiler: return→raise, def→guard, repeat while/until dispatch.
Runtime: hs-repeat-while, hs-repeat-until.
Test gen: script block extraction for def functions.
repeat suite: 10→13/30.

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

lib/hyperscript/parser.sx

@@ -1041,7 +1041,7 @@
           (let
             ((cnd (parse-expr)))
             (let
-              ((then-body (parse-cmd-list)))
+              ((then-body (do (match-kw "then") (parse-cmd-list))))
               (let
                 ((else-body (if (or (match-kw "else") (match-kw "otherwise")) (parse-cmd-list) nil)))
                 (match-kw "end")