fix(led-tool): harden Web Serial raw REPL connect

Improve boot wait, readUntil buffer handling, and settings editor
host/Web Serial flows after device reset.

Co-authored-by: Cursor <cursoragent@cursor.com>

static/settings_editor.html

@@ -185,10 +185,11 @@
         document.body.getAttribute('data-api-base') ??
         (location.pathname.includes('/led-tool') ? '/led-tool' : '');
       const prefix = api + '/static';
+      const v = '20260520';
       function loadScript(url) {
         return new Promise((resolve, reject) => {
           const s = document.createElement('script');
-          s.src = url;
+          s.src = url + (url.includes('?') ? '&' : '?') + 'v=' + v;
           s.onload = () => resolve();
           s.onerror = () => reject(new Error('Failed to load ' + url));
           document.body.appendChild(s);