Delete sx_ref.py — OCaml is the sole SX evaluator

Removes the 5993-line bootstrapped Python evaluator (sx_ref.py) and all
code that depended on it exclusively. Both bootstrappers (JS + OCaml)
now use a new synchronous OCaml bridge (ocaml_sync.py) to run the
transpiler. JS build produces identical output; OCaml bootstrap produces
byte-identical sx_ref.ml.

Key changes:
- New shared/sx/ocaml_sync.py: sync subprocess bridge to sx_server.exe
- hosts/javascript/bootstrap.py: serialize defines → temp file → OCaml eval
- hosts/ocaml/bootstrap.py: same pattern for OCaml transpiler
- shared/sx/{html,async_eval,resolver,jinja_bridge,handlers,pages,deps,helpers}:
  stub or remove sx_ref imports; runtime uses OCaml bridge (SX_USE_OCAML=1)
- sx/sxc/pages: parse defpage/defhandler from AST instead of Python eval
- hosts/ocaml/lib/sx_primitives.ml: append handles non-list 2nd arg per spec
- Deleted: sx_ref.py, async_eval_ref.py, 6 Python test runners, misc ref/ files

Test results: JS 1078/1078, OCaml 1114/1114.
sx_docs SSR has pre-existing rendering issues to investigate separately.

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

shared/sx/resolver.py

@@ -31,7 +31,10 @@ import asyncio
 from typing import Any
 
 from .types import Component, Keyword, Lambda, NIL, Symbol
-from .ref.sx_ref import eval_expr as _raw_eval, trampoline as _trampoline
+# sx_ref.py removed — stub so module loads. OCaml bridge handles evaluation.
+def _not_available(*a, **kw):
+    raise RuntimeError("sx_ref.py has been removed — use SX_USE_OCAML=1")
+_raw_eval = _trampoline = _not_available
 
 def _eval(expr, env):
     """Evaluate and unwrap thunks — all resolver.py _eval calls are non-tail."""