Revert WIP hydration commit — undefined hydrate-start!/stop! broke all islands

The WIP commit (0044f17e) added calls to hydrate-start!, hydrate-stop!,
hydrate-push!, hydrate-pop!, and hydrate-next-*! — none of which were
ever defined. This crashed hydrate-island silently (cek-try swallowed
the error), preventing event listener attachment on every island.

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

web/boot.sx

@@ -55,8 +55,6 @@
                 (dom-append-to-head el)))))
         els))))
 
-(define *hydrating* false)
-
 (define
   sx-mount
   :effects (mutation io)
@@ -331,14 +329,9 @@
                     p
                     (if (dict-has? kwargs p) (dict-get kwargs p) nil)))
                 (component-params comp))
-              (do
-                (hydrate-start! el)
-                (log-info "  hydrate-start done")
-                (with-island-scope
-                  (fn (disposable) (append! disposers disposable))
-                  (fn () (render-to-dom (component-body comp) local nil)))
-                (log-info "  render-to-dom done")
-                (hydrate-stop!)
+              (let
+                ((body-dom (cek-try (fn () (with-island-scope (fn (disposable) (append! disposers disposable)) (fn () (render-to-dom (component-body comp) local nil)))) (fn (err) (log-warn (str "hydrate-island FAILED: " comp-name " — " err)) (let ((error-el (dom-create-element "div" nil))) (dom-set-attr error-el "class" "sx-island-error") (dom-set-attr error-el "style" "padding:8px;margin:4px 0;border:1px solid #ef4444;border-radius:4px;background:#fef2f2;color:#b91c1c;font-family:monospace;font-size:12px;white-space:pre-wrap") (dom-set-text-content error-el (str "Island error: " comp-name "\n" err)) error-el)))))
+                (host-call el "replaceChildren" body-dom)
                 (dom-set-data el "sx-disposers" disposers)
                 (set-timeout (fn () (process-elements el)) 0)
                 (log-info