js-on-sx: NaN / Infinity resolve at transpile; strict-eq returns false for NaN

Previously NaN / Infinity were SX symbols that couldn't be (define)'d
because the SX tokenizer parses 'NaN' and 'Infinity' as numeric literals.

js-transpile-ident now rewrites NaN -> (js-nan-value), Infinity ->
(js-infinity-value), each a zero-arg function returning the appropriate
IEEE value ((/ 0.0 0.0) and (/ 1.0 0.0)).

Also fixes js-number-is-nan: in this SX, (= nan nan) returns true, so the
classic 'v !== v' trick doesn't work. Now checks (inspect v) against
'nan'/'-nan' strings.

Extends js-strict-eq: NaN === NaN returns false per ES spec.

8 new unit tests, 497/499 total.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/js/test.sh

@@ -1213,6 +1213,24 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 3709)
 (eval "(js-eval \"var a=[1,2,3]; a.keys().join(',')\")")
 
+;; ── Phase 11.globals: NaN / Infinity / strict-eq ─────────────
+(epoch 3750)
+(eval "(js-eval \"typeof NaN\")")
+(epoch 3751)
+(eval "(js-eval \"isNaN(NaN)\")")
+(epoch 3752)
+(eval "(js-eval \"isNaN(5)\")")
+(epoch 3753)
+(eval "(js-eval \"NaN === NaN\")")
+(epoch 3754)
+(eval "(js-eval \"Infinity > 100\")")
+(epoch 3755)
+(eval "(js-eval \"-Infinity < 0\")")
+(epoch 3756)
+(eval "(js-eval \"isFinite(1)\")")
+(epoch 3757)
+(eval "(js-eval \"isFinite(Infinity)\")")
+
 ;; ── Phase 11.strmore: more String.prototype methods ─────────
 (epoch 3800)
 (eval "(js-eval \"'hello'.at(0)\")")
@@ -1909,6 +1927,16 @@ check 3707 "arr.toReversed"                '"2,1,3"'
 check 3708 "arr.toSorted"                  '"1,1,3,4,5"'
 check 3709 "arr.keys"                      '"0,1,2"'
 
+# ── Phase 11.globals: NaN / Infinity / strict-eq ─────────────
+check 3750 "typeof NaN"                    '"number"'
+check 3751 "isNaN(NaN)"                    'true'
+check 3752 "isNaN(5)"                      'false'
+check 3753 "NaN === NaN"                   'false'
+check 3754 "Infinity > 100"                'true'
+check 3755 "-Infinity < 0"                 'true'
+check 3756 "isFinite(1)"                   'true'
+check 3757 "isFinite(Infinity)"            'false'
+
 # ── Phase 11.strmore: more String.prototype methods ───────────
 check 3800 "'hello'.at(0)"                 '"h"'
 check 3801 "'hello'.at(-1)"                '"o"'