Fix JIT closure isolation, SX wire format, server diagnostics

Root cause: _env_bind_hook mirrored ALL env_bind calls (including
lambda parameter bindings) to the shared VM globals table. Factory
functions like make-page-fn that return closures capturing different
values for the same param names (default-name, prefix, suffix) would
have the last call's values overwrite all previous closures' captured
state in globals. OP_GLOBAL_GET reads globals first, so all closures
returned the last factory call's values.

Fix: only sync root-env bindings (parent=None) to VM globals. Lambda
parameter bindings stay in their local env, found via vm_closure_env
fallback in OP_GLOBAL_GET.

Also in this commit:
- OP_CLOSURE propagates parent vm_closure_env to child closures
- Remove JIT globals injection (closure vars found via env chain)
- sx_server.ml: SX-Request header → returns text/sx (aser only)
- sx_server.ml: diagnostic endpoint GET /sx/_debug/{env,eval,route}
- sx_server.ml: page helper stubs for deep page rendering
- sx_server.ml: skip client-libs/ dir (browser-only definitions)
- adapter-html.sx: unknown components → HTML comment (not error)
- sx-platform.js: .sxbc fallback loader for bytecode modules
- Delete sx_http.ml (standalone HTTP server, unused)
- Delete stale .sxbc.json files (arity=0 bug, replaced by .sxbc)
- 7 new closure isolation tests in test-closure-isolation.sx
- mcp_tree.ml: emit arity + upvalue-count in .sxbc.json output

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

shared/static/wasm/sx/signals.sx

@@ -35,25 +35,9 @@
 ;; Named stores — page-level signal containers
 ;; --------------------------------------------------------------------------
 
-(define *store-registry* (dict))
-
-(define def-store :effects [mutation]
-  (fn ((name :as string) (init-fn :as lambda))
-    (let ((registry *store-registry*))
-      (when (not (has-key? registry name))
-        (set! *store-registry* (assoc registry name (cek-call init-fn nil))))
-      (get *store-registry* name))))
-
-(define use-store :effects []
-  (fn ((name :as string))
-    (if (has-key? *store-registry* name)
-      (get *store-registry* name)
-      (error (str "Store not found: " name
-                  ". Call (def-store ...) before (use-store ...).")))))
-
-(define clear-stores :effects [mutation]
-  (fn ()
-    (set! *store-registry* (dict))))
+;; def-store, use-store, clear-stores are now OCaml primitives
+;; (sx_primitives.ml) with a global mutable registry that survives
+;; env scoping across bytecode modules and island hydration.
 
 
 ;; --------------------------------------------------------------------------