feat: Add dynamic loading of JSZip library with error handling for EPUB fetching

abogen/web/templates/reader_embed.html

@@ -178,6 +178,7 @@
     </div>
   </div>
   <script type="application/json" id="reader-data">{{ {'chapters': chapters, 'title': job.original_filename}|tojson }}</script>
+  <script src="https://cdn.jsdelivr.net/npm/jszip@3.10.1/dist/jszip.min.js"></script>
   <script src="https://cdn.jsdelivr.net/npm/epubjs@0.3.93/dist/epub.min.js"></script>
   <script type="module">
     const statusEl = document.querySelector('[data-role="reader-status"]');
@@ -306,6 +307,30 @@
       return buffer;
     };
 
+    let ensureJsZipPromise = null;
+    const ensureJsZip = async () => {
+      if (typeof window !== 'undefined' && window.JSZip) {
+        return window.JSZip;
+      }
+      if (ensureJsZipPromise) {
+        return ensureJsZipPromise;
+      }
+      ensureJsZipPromise = (async () => {
+        try {
+          const module = await import('https://cdn.jsdelivr.net/npm/jszip@3.10.1/+esm');
+          const lib = module?.default || module?.JSZip || module;
+          if (lib && typeof window !== 'undefined') {
+            window.JSZip = lib;
+          }
+          return lib || null;
+        } catch (error) {
+          console.error('Failed to dynamically import JSZip', error);
+          return null;
+        }
+      })();
+      return ensureJsZipPromise;
+    };
+
     const buildAssetUrl = (path) => {
       if (!path) {
         return '';
@@ -830,6 +855,12 @@
         return;
       }
 
+      const jszipLib = await ensureJsZip();
+      if (!jszipLib) {
+        setStatus('JSZip could not be loaded. Please check your network connection.');
+        return;
+      }
+
       setStatus('Fetching EPUB…');
       let epubPayload = null;