Fix process-bindings scope loss and async-invoke arity, bootstrap async adapter

Two bugs fixed:
1. process-bindings used merge(env) which returns {} for Env objects
   (Env is not a dict subclass). Changed to env-extend in render.sx
   and adapter-async.sx. This caused "Undefined symbol: theme" etc.
2. async-aser-eval-call passed evaled-args list to async-invoke(&rest),
   double-wrapping it. Changed to inline apply + coroutine check.

Also: bootstrap define-async into sx_ref.py (Phase 6), replace ~1000 LOC
hand-written async_eval_ref.py with 24-line thin re-export shim.

Test runner now uses Env (not flat dict) for render envs to catch scope bugs.
8 new regression tests (4 scope chain, 2 native callable arity, 2 render).

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

shared/sx/ref/boot.sx

@@ -344,15 +344,15 @@
 (define hydrate-island
   (fn (el)
     (let ((name (dom-get-attr el "data-sx-island"))
-          (state-json (or (dom-get-attr el "data-sx-state") "{}")))
+          (state-sx (or (dom-get-attr el "data-sx-state") "{}")))
       (let ((comp-name (str "~" name))
             (env (get-render-env nil)))
         (let ((comp (env-get env comp-name)))
           (if (not (or (component? comp) (island? comp)))
             (log-warn (str "hydrate-island: unknown island " comp-name))
 
-            ;; Parse state and build keyword args
-            (let ((kwargs (json-parse state-json))
+            ;; Parse state and build keyword args — SX format, not JSON
+            (let ((kwargs (or (first (sx-parse state-sx)) {}))
                   (disposers (list))
                   (local (env-merge (component-closure comp) env)))
 
@@ -494,8 +494,8 @@
 ;;   (log-info msg)                → void (console.log with prefix)
 ;;   (log-parse-error label text err) → void (diagnostic parse error)
 ;;
-;; === JSON ===
-;;   (json-parse str)              → dict/list/value (JSON.parse)
+;; === Parsing (island state) ===
+;;   (sx-parse str)                → list of AST expressions (from parser.sx)
 ;;
 ;; === Processing markers ===
 ;;   (mark-processed! el key)      → void