Complete Python eval removal: epoch protocol, scope consolidation, JIT fixes

Route all rendering through OCaml bridge — render_to_html no longer uses
Python async_eval. Fix register_components to parse &key params and &rest
children from defcomp forms. Remove all dead sx_ref.py imports.

Epoch protocol (prevents pipe desync):
- Every command prefixed with (epoch N), all responses tagged with epoch
- Both sides discard stale-epoch messages — desync structurally impossible
- OCaml main loop discards stale io-responses between commands

Consolidate scope primitives into sx_scope.ml:
- Single source of truth for scope-push!/pop!/peek, collect!/collected,
  emit!/emitted, context, and 12 other scope operations
- Removes duplicate registrations from sx_server.ml (including bugs where
  scope-emit! and clear-collected! were registered twice with different impls)
- Bind scope prims into env so JIT VM finds them via OP_GLOBAL_GET

JIT VM fixes:
- Trampoline thunks before passing args to CALL_PRIM
- as_list resolves thunks via _sx_trampoline_fn
- len handles all value types (Bool, Number, RawHTML, SxExpr, Spread, etc.)

Other fixes:
- ~cssx/tw signature: (tokens) → (&key tokens) to match callers
- Minimal Python evaluator in html.py for sync sx() Jinja function
- Python scope primitive stubs (thread-local) for non-OCaml paths
- Reader macro resolution via OcamlSync instead of sx_ref.py

Tests: 1114 OCaml, 1078 JS, 35 Python regression, 6/6 Playwright SSR

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

shared/sx/deps.py

@@ -152,18 +152,11 @@ def transitive_deps(name: str, env: dict[str, Any]) -> set[str]:
     Returns the set of all component names (with ~ prefix) that
     *name* can transitively render, NOT including *name* itself.
     """
-    if _use_ref():
-        from .ref.sx_ref import transitive_deps as _ref_td
-        return set(_ref_td(name, env))
     return _transitive_deps_fallback(name, env)
 
 
 def compute_all_deps(env: dict[str, Any]) -> None:
     """Compute and cache deps for all Component entries in *env*."""
-    if _use_ref():
-        from .ref.sx_ref import compute_all_deps as _ref_cad
-        _ref_cad(env)
-        return
     _compute_all_deps_fallback(env)
 
 
@@ -172,9 +165,6 @@ def scan_components_from_sx(source: str) -> set[str]:
 
     Returns names with ~ prefix, e.g. {"~card", "~shared:layout/nav-link"}.
     """
-    if _use_ref():
-        from .ref.sx_ref import scan_components_from_source as _ref_sc
-        return set(_ref_sc(source))
     return _scan_components_from_sx_fallback(source)
 
 
@@ -183,18 +173,11 @@ def components_needed(page_sx: str, env: dict[str, Any]) -> set[str]:
 
     Returns names with ~ prefix.
     """
-    if _use_ref():
-        from .ref.sx_ref import components_needed as _ref_cn
-        return set(_ref_cn(page_sx, env))
     return _components_needed_fallback(page_sx, env)
 
 
 def compute_all_io_refs(env: dict[str, Any], io_names: set[str]) -> None:
     """Compute and cache transitive IO refs for all Component entries in *env*."""
-    if _use_ref():
-        from .ref.sx_ref import compute_all_io_refs as _ref_cio
-        _ref_cio(env, list(io_names))
-        return
     _compute_all_io_refs_fallback(env, io_names)