Restore hyperscript work on stable site base (908f4f80)

Reset to last known-good state (908f4f80) where links, stepper, and
islands all work, then recovered all hyperscript implementation,
conformance tests, behavioral tests, Playwright specs, site sandbox,
IO-aware server loading, and upstream test suite from f271c88a.

Excludes runtime changes (VM resolve hook, VmSuspended browser handler,
sx_ref.ml guard recovery) that need careful re-integration.

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

shared/static/wasm/sx/boot.sx

@@ -444,7 +444,6 @@
       (sx-hydrate-islands nil)
       (run-post-render-hooks)
       (flush-collected-styles)
-      (hs-boot!)
       (set-timeout (fn () (process-elements nil)) 0)
       (dom-set-attr
         (host-get (dom-document) "documentElement")