Unify CEK callable dispatch, add named-let transpiler, full stdlib

Three changes that together enable the full 46-function stdlib migration:

1. CEK callable unification (spec/evaluator.sx):
   cek-call now routes both native callables and SX lambdas through
   continue-with-call, so replacing a native function with an SX lambda
   doesn't change shift/reset behavior.

2. Named-let transpiler support (hosts/javascript/transpiler.sx):
   (let loop ((i 0)) body...) now transpiles to a named IIFE:
   (function loop(i) { body })(0)
   This was the cause of the 3 test regressions (produced [object Object]).

3. Full stdlib via runtime eval (hosts/javascript/bootstrap.py):
   stdlib.sx is eval'd at runtime (not transpiled) so its defines go
   into PRIMITIVES without shadowing module-scope variables that the
   transpiled evaluator uses directly.

stdlib.sx now contains all 46 library functions:
  Logic: not
  Comparison: != <= >= eq? eqv? equal?
  Predicates: boolean? number? string? list? dict? continuation?
    zero? odd? even? empty?
  Arithmetic: inc dec abs ceil round min max clamp
  Collections: first last rest nth cons append reverse flatten
    range chunk-every zip-pairs
  Dict: vals has-key? assoc dissoc into
  Strings: upcase downcase string-length substring string-contains?
    starts-with? ends-with? split join replace contains?
  Text: pluralize escape parse-datetime assert

All hosts: JS 957+1080, Python 744, OCaml 952 — zero regressions.

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

hosts/javascript/platform.py

@@ -1412,6 +1412,11 @@ PLATFORM_JS_POST = '''
   var get = PRIMITIVES["get"];
   var assoc = PRIMITIVES["assoc"];
   var range = PRIMITIVES["range"];
+  var floor = PRIMITIVES["floor"];
+  var pow = PRIMITIVES["pow"];
+  var mod = PRIMITIVES["mod"];
+  var indexOf_ = PRIMITIVES["index-of"];
+  var hasKey = PRIMITIVES["has-key?"];
   function zip(a, b) { var r = []; for (var i = 0; i < Math.min(a.length, b.length); i++) r.push([a[i], b[i]]); return r; }
   function append_b(arr, x) { arr.push(x); return arr; }
   var apply = function(f, args) {
@@ -1802,7 +1807,7 @@ PLATFORM_DOM_JS = """
 
   // Wire CEK render hooks — evaluator checks _renderCheck/_renderFn instead of
   // the old renderActiveP()/isRenderExpr()/renderExpr() triple.
-  _renderCheck = function(expr, env) { return isRenderExpr(expr); };
+  _renderCheck = function(expr, env) { return _renderMode && isRenderExpr(expr); };
   _renderFn = function(expr, env) { return renderToDom(expr, env, null); };
 
   var SVG_NS = "http://www.w3.org/2000/svg";