fix: reader header auto-hide, keyboard null guard, active thumb box-shadow

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

app/static/js/reader.js

@@ -2,7 +2,7 @@
 'use strict';
 
 document.addEventListener('DOMContentLoaded', () => {
-  const { startPage, totalPages } = window.readerConfig || { startPage: 1, totalPages: 1 };
+  const { startPage } = window.readerConfig || { startPage: 1 };
 
   // Elements
   // #readerContent is the actual scroll container (overflow-y: auto)
@@ -122,7 +122,10 @@ document.addEventListener('DOMContentLoaded', () => {
   }
 
   // Show header on mouse move
-  document.addEventListener('mousemove', showHeader);
+  document.addEventListener('mousemove', () => {
+    showHeader();
+    scheduleHideHeader();
+  });
 
   // -------------------------
   // Jump to page
@@ -185,6 +188,7 @@ document.addEventListener('DOMContentLoaded', () => {
   // -------------------------
   document.addEventListener('keydown', (e) => {
     if (e.target.tagName === 'INPUT' || e.target.tagName === 'SELECT') return;
+    if (!readerContent) return;
     showHeader();
 
     switch (e.key) {