SX renderer: adapter-html.sx as sole renderer, conditions, pattern matching

Evaluator: conditions/restarts, pattern matching, render-trace support.
adapter-html.sx: full SX-defined HTML renderer replacing native OCaml.
spec/render.sx: updated render mode helpers.
sx_browser.ml: use SX render-to-html instead of native.
sx_ref.ml: evaluator updates for conditions + match.
Bootstrap + transpiler updates for new forms.

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

hosts/ocaml/bin/integration_tests.ml

@@ -407,7 +407,7 @@ let () =
   let render_html src =
     let exprs = Sx_parser.parse_all src in
     let expr = match exprs with [e] -> e | _ -> Nil in
-    Sx_render.render_to_html expr env
+    Sx_render.sx_render_to_html env expr env
   in
 
   (* Helper: call SX render-to-html via the adapter *)