Delete evaluator.py shim: all imports go directly to bootstrapped sx_ref.py

EvalError moved to types.py. All 27 files updated to import eval_expr,
trampoline, call_lambda, etc. directly from shared.sx.ref.sx_ref instead
of through the evaluator.py indirection layer. 320/320 spec tests pass.

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

shared/sx/tests/test_bootstrapper.py

@@ -21,7 +21,7 @@ class TestJsSxTranslation:
 
     def _translate(self, sx_source: str) -> str:
         """Translate a single SX expression to JS using js.sx."""
-        from shared.sx.evaluator import evaluate
+        from shared.sx.ref.sx_ref import evaluate
         env = load_js_sx()
         expr = parse(sx_source)
         env["_def_expr"] = expr