js-on-sx: parser handles comma operator (a, b, c)

Was failing with "Expected punct ')' got punct ','" because the
paren handler only consumed a single assignment. Added
jp-parse-comma-seq helpers that build a js-comma AST node with
the expression list; transpiler emits (begin ...) so each is
evaluated in order and the last value is returned.
built-ins/Object: 44/50 → 46/50. conformance.sh: 148/148.

lib/js/test262-scoreboard.md

@@ -1,24 +1,22 @@
 # test262 scoreboard
 
 Pinned commit: `d5e73fc8d2c663554fb72e2380a8c2bc1a318a33`
-Wall time: 71.0s
+Wall time: 64.1s
 
-**Total:** 46/50 runnable passed (92.0%). Raw: pass=46 fail=2 skip=0 timeout=2 total=50.
+**Total:** 46/50 runnable passed (92.0%). Raw: pass=46 fail=4 skip=0 timeout=0 total=50.
 
 ## Top failure modes
 
-- **2x** Timeout
-- **2x** Test262Error (assertion failed)
+- **4x** ReferenceError (undefined symbol)
 
 ## Categories (worst pass-rate first, min 10 runnable)
 
 | Category | Pass | Fail | Skip | Timeout | Total | Pass % |
 |---|---:|---:|---:|---:|---:|---:|
-| built-ins/Number | 46 | 2 | 0 | 2 | 50 | 92.0% |
+| built-ins/Object | 46 | 4 | 0 | 0 | 50 | 92.0% |
 
 ## Per-category top failures (min 10 runnable, worst first)
 
-### built-ins/Number  (46/50 — 92.0%)
+### built-ins/Object  (46/50 — 92.0%)
 
-- **2x** Timeout
-- **2x** Test262Error (assertion failed)
+- **4x** ReferenceError (undefined symbol)