Harmonize navigation and modals across cookbook & shopping list, fix WebSocket proxying, and add PWA offline support

app/templates/cookbook.html

@@ -4,7 +4,13 @@
   <meta charset="UTF-8">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <title>Mein Kochbuch – What To Cook?</title>
-  <link rel="stylesheet" href="/static/cookbook.css?v=4.5.4">
+  <link rel="manifest" href="/manifest.json">
+  <meta name="theme-color" content="#1E4D3B">
+  <meta name="apple-mobile-web-app-capable" content="yes">
+  <meta name="apple-mobile-web-app-status-bar-style" content="default">
+  <meta name="apple-mobile-web-app-title" content="What To Cook?">
+  <link rel="apple-touch-icon" href="/static/icon-192.png">
+  <link rel="stylesheet" href="/static/cookbook.css?v=4.6.1">
   <link rel="icon" href="data:image/svg+xml,<svg xmlns=%22http://www.w3.org/2000/svg%22 viewBox=%220 0 100 100%22><text y=%22.9em%22 font-size=%2290%22>📖</text></svg>">
   <style id="print-engine-styles">
     /* Auf dem Bildschirm: Cover, Inhaltsverzeichnis und Seitenzahlen ausblenden */
@@ -2717,6 +2723,12 @@
         openRecipeModal();
       }
     });
+
+    if ('serviceWorker' in navigator) {
+      window.addEventListener('load', () => {
+        navigator.serviceWorker.register('/sw.js').catch(err => console.log('SW register fail:', err));
+      });
+    }
   </script>
 </body>
 </html>

app/templates/home.html

@@ -4,6 +4,12 @@
   <meta charset="UTF-8">
   <meta name="viewport" content="width=device-width, initial-scale=1.0, viewport-fit=cover">
   <title>What To Cook? – Menü</title>
+  <link rel="manifest" href="/manifest.json">
+  <meta name="theme-color" content="#1E4D3B">
+  <meta name="apple-mobile-web-app-capable" content="yes">
+  <meta name="apple-mobile-web-app-status-bar-style" content="default">
+  <meta name="apple-mobile-web-app-title" content="What To Cook?">
+  <link rel="apple-touch-icon" href="/static/icon-192.png">
   <link rel="stylesheet" href="/static/cookbook.css?v=4.6.1">
   <link rel="icon" href="data:image/svg+xml,<svg xmlns=%22http://www.w3.org/2000/svg%22 viewBox=%220 0 100 100%22><text y=%22.9em%22 font-size=%2290%22>🍽️</text></svg>">
   <style>
@@ -289,5 +295,12 @@
 
   </main>
 
+  <script>
+    if ('serviceWorker' in navigator) {
+      window.addEventListener('load', () => {
+        navigator.serviceWorker.register('/sw.js').catch(err => console.log('SW register fail:', err));
+      });
+    }
+  </script>
 </body>
 </html>