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/compiler.sx

@@ -691,7 +691,7 @@
                   (and
                     (not (empty? rest-args))
                     (= (type-of (first rest-args)) "keyword"))
-                  (letrec
+                  (let
                     ((skip-annotations (fn (items) (if (empty? items) nil (if (= (type-of (first items)) "keyword") (skip-annotations (rest (rest items))) (first items))))))
                     (skip-annotations rest-args))
                   (first rest-args)))))