feat: add user instructions to viewer popup

src/viewer/index.js

@@ -34,10 +34,26 @@ const openBtn = document.getElementById('open-btn');
 const statusEl = document.getElementById('status');
 const listEl = document.getElementById('video-list');
 const btnRow = document.getElementById('btn-row');
+const instructionsToggle = document.getElementById('instructions-toggle');
+const instructionsBody = document.getElementById('instructions-body');
 
 listEl.style.wordBreak = 'break-word';
 listEl.style.whiteSpace = 'pre-wrap';
 
+function setInstructionsExpanded(expanded) {
+  if (!instructionsToggle || !instructionsBody) return;
+  instructionsBody.hidden = !expanded;
+  instructionsToggle.setAttribute('aria-expanded', String(expanded));
+  instructionsToggle.textContent = expanded ? 'Hide instructions' : 'Show instructions';
+}
+
+if (instructionsToggle && instructionsBody) {
+  setInstructionsExpanded(true);
+  instructionsToggle.addEventListener('click', () => {
+    setInstructionsExpanded(instructionsBody.hidden);
+  });
+}
+
 /* ======================================================================== */
 /* UI helpers                                                               */
 /* ======================================================================== */