Unknown components throw instead of rendering error box

render-dom-unknown-component now calls (error ...) instead of
creating a styled div. This lets tryEvalContent catch the error
and fall back to server fetch, instead of rendering "Unknown
component: ~name" into the page.

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

shared/sx/ref/adapter-dom.sx

@@ -286,11 +286,7 @@
 
 (define render-dom-unknown-component
   (fn (name)
-    (let ((el (dom-create-element "div" nil)))
-      (dom-set-attr el "style"
-        "background:#fef2f2;border:1px solid #fca5a5;color:#991b1b;padding:4px 8px;margin:2px;border-radius:4px;font-size:12px;font-family:monospace")
-      (dom-append el (create-text-node (str "Unknown component: " name)))
-      el)))
+    (error (str "Unknown component: " name))))
 
 
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