feat: add interactive HTML export and verification

tests/engine_interact.js

@@ -0,0 +1,49 @@
+// Interactive smoke test: verify click -> navigate flow works.
+const fs = require('fs');
+const html = fs.readFileSync(process.argv[2], 'utf-8');
+const m = html.match(/<script>\s*(window\.QUX_MODEL.*?)<\/script>/s);
+if (!m) { console.error('no engine'); process.exit(1); }
+
+function makeEl() {
+  const el = {
+    style: {}, dataset: {}, children: [], _listeners: {},
+    classList: { add() {}, remove() {} },
+    appendChild(c) { el.children.push(c); return c; },
+    addEventListener(t, fn) { (el._listeners[t] = el._listeners[t] || []).push(fn); },
+    set textContent(v) { el._text = v; }, get textContent() { return el._text || ''; },
+    set innerHTML(v) { el._html = v; }, get innerHTML() { return el._html || ''; },
+  };
+  return el;
+}
+const stage = makeEl();
+const nameEl = makeEl();
+global.window = { innerWidth: 1920, innerHeight: 1080, addEventListener() {} };
+global.document = {
+  getElementById(id) { return id === 'stage' ? stage : (id === 'screenName' ? nameEl : makeEl()); },
+  createElement() { return makeEl(); },
+};
+
+eval(m[1]);
+
+const firstScreenName = nameEl._text;
+const wired = [];
+(function collect(el) {
+  if (el._listeners.click && el._listeners.click.length) wired.push(el);
+  el.children.forEach(collect);
+})(stage);
+
+console.log('start screen:', firstScreenName);
+console.log('clickable (wired) widgets on screen:', wired.length);
+
+if (wired.length) {
+  wired[0]._listeners.click[0](); // simulate click
+  const after = nameEl._text;
+  console.log('after click screen:', after);
+  if (after && after !== firstScreenName) {
+    console.log('INTERACTION OK: navigated', firstScreenName, '->', after);
+  } else {
+    console.log('note: click stayed on same screen (or target is same screen) -', after);
+  }
+} else {
+  console.log('no wired widgets on start screen (no interactions starting here)');
+}