Dynamic IO proxy: derive proxied primitives from component io_refs

Replace hardcoded IO primitive lists on both client and server with
data-driven registration. Page registry entries carry :io-deps (list
of IO primitive names) instead of :has-io boolean. Client registers
proxied IO on demand per page via registerIoDeps(). Server builds
allowlist from component analysis.

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

shared/sx/ref/boot.sx

@@ -344,7 +344,6 @@
       (log-info (str "sx-browser " SX_VERSION))
       (init-css-tracking)
       (init-style-dict)
-      (init-io-primitives)
       (process-page-scripts)
       (process-sx-scripts nil)
       (sx-hydrate-elements nil)