IO registry: defio declares platform suspension points

Core SX has zero IO — platforms extend __io-registry via (defio name
:category :data/:code/:effect ...). The server web platform declares 44
operations in web/io.sx. batchable_helpers now derived from registry
(:batchable true) instead of hardcoded list. Startup validation warns if
bound IO ops lack registry entries. Browser gets empty registry, ready
for step 5 (IO suspension).

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

shared/static/wasm/sx/boot.sx

@@ -425,7 +425,6 @@
     ()
     (do
       (log-info (str "sx-browser " SX_VERSION))
-      (init-css-tracking)
       (process-page-scripts)
       (process-sx-scripts nil)
       (sx-hydrate-elements nil)
@@ -433,7 +432,6 @@
       (run-post-render-hooks)
       (flush-collected-styles)
       (set-timeout (fn () (process-elements nil)) 0)
-      (dom-listen (dom-window) "popstate" (fn (e) (handle-popstate 0)))
       (dom-set-attr
         (host-get (dom-document) "documentElement")
         "data-sx-ready"