js-on-sx: Object.__callable__ returns this for new Object() no-args

js-new-call Object had set obj.__proto__ correctly, but then the
__callable__ returned a fresh (dict), which js-new-call's "use
returned dict over obj" rule honoured — losing the proto. Added
is-new check (this.__proto__ === Object.prototype) and return
this instead of a new dict when invoked as a constructor with
no/null args. Now new Object().__proto__ === Object.prototype.
built-ins/Object: 37/50 → 41/50. conformance.sh: 148/148.

lib/js/test262-scoreboard.md

@@ -1,28 +1,28 @@
 # test262 scoreboard
 
 Pinned commit: `d5e73fc8d2c663554fb72e2380a8c2bc1a318a33`
-Wall time: 226.1s
+Wall time: 37.1s
 
-**Total:** 78/99 runnable passed (78.8%). Raw: pass=78 fail=15 skip=1 timeout=6 total=100.
+**Total:** 41/50 runnable passed (82.0%). Raw: pass=41 fail=9 skip=0 timeout=0 total=50.
 
 ## Top failure modes
 
-- **13x** Test262Error (assertion failed)
-- **6x** Timeout
-- **1x** ReferenceError (undefined symbol)
-- **1x** SyntaxError (parse/unsupported syntax)
+- **4x** ReferenceError (undefined symbol)
+- **2x** SyntaxError (parse/unsupported syntax)
+- **2x** Test262Error (assertion failed)
+- **1x** runner-error: sx_server closed stdout mid-epoch
 
 ## Categories (worst pass-rate first, min 10 runnable)
 
 | Category | Pass | Fail | Skip | Timeout | Total | Pass % |
 |---|---:|---:|---:|---:|---:|---:|
-| built-ins/String | 78 | 15 | 1 | 6 | 100 | 78.8% |
+| built-ins/Object | 41 | 9 | 0 | 0 | 50 | 82.0% |
 
 ## Per-category top failures (min 10 runnable, worst first)
 
-### built-ins/String  (78/99 — 78.8%)
+### built-ins/Object  (41/50 — 82.0%)
 
-- **13x** Test262Error (assertion failed)
-- **6x** Timeout
-- **1x** ReferenceError (undefined symbol)
-- **1x** SyntaxError (parse/unsupported syntax)
+- **4x** ReferenceError (undefined symbol)
+- **2x** SyntaxError (parse/unsupported syntax)
+- **2x** Test262Error (assertion failed)
+- **1x** runner-error: sx_server closed stdout mid-epoch