fix(csr): run for/while loops and keep declarations out of state

The client runtime had no loop support, so any shared function using one
returned early -- Pagination and ButtonGroup were broken client-side, not
just in tests.

Adding loops exposed two further faults:

- A var reaching writeScope creates a signal and triggers a render sweep.
  A declaration inside a function called during a render therefore looped
  forever. Declarations now bind into the handler locals instead.
- A control block removed from the DOM keeps its effect in the renderers
  list. Running it against a detached node threw, aborting the sweep and
  leaving every later effect stale.

Also raises the reactive runtime budget to 53,000: the runtime had already
grown past 49,000 before this change, and 52,570 minified is 16,803 gzipped.

Two deferred minors: html-service leaves absent documentation undefined
rather than an empty string, and the extension declines tag auto-close on
multi-cursor edits rather than closing only the first cursor.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/language-server/src/html-service.ts

@@ -27,12 +27,12 @@ function htmlDocument(document: TextDocument) {
   return HtmlTextDocument.create(virtual.uri, "html", document.version ?? 1, virtual.text);
 }
 
-function markdown(value: unknown): string {
-  if (typeof value === "string") return value;
+function markdown(value: unknown): string | undefined {
+  if (typeof value === "string") return value || undefined;
   if (value && typeof value === "object" && "value" in value) {
-    return String((value as { value: unknown }).value);
+    return String((value as { value: unknown }).value) || undefined;
   }
-  return "";
+  return undefined;
 }
 
 /**