js-on-sx: wrapper constructor-detection, Array.prototype.toString, >>> operator

Number.__callable__ and String.__callable__ now check this.__proto__ ===
Number/String.prototype before writing wrapper slots, preventing false-positive
mutation when called as plain function. js-to-number extended to unwrap
wrapper dicts and call valueOf/toString for plain objects. Array.prototype.toString
replaced with a direct js-list-join implementation (eliminates infinite recursion
via js-invoke-method on dict-based arrays). >>> added to transpiler + runtime.

String test262 subset: 62→66/100. 529/530 unit, 147/148 slice.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/js/transpile.sx

@@ -295,6 +295,11 @@
               (list (js-sym "js-undefined?") (js-sym "_a")))
             (js-transpile r)
             (js-sym "_a"))))
+      ((= op ">>>")
+        (list
+          (js-sym "js-unsigned-rshift")
+          (js-transpile l)
+          (js-transpile r)))
       (else (error (str "js-transpile-binop: unsupported op: " op))))))
 
 ;; ── Object literal ────────────────────────────────────────────────