Implement Chromium-based PDF generation service; add fetchAndDownloadPdf utility and update contract generation endpoint

src/FrontOffice.Main/Pages/_Host.cshtml

@@ -35,7 +35,31 @@
     <!-- Load MudBlazor JS before Blazor to avoid early JS interop calls failing; add cache-busting -->
     <script src="_content/MudBlazor/MudBlazor.min.js" asp-append-version="true"></script>
     <script src="_framework/blazor.server.js"></script>
-    <script src="/js/print-utils.js" asp-append-version="true"></script>
+    <script>
+        window.fetchAndDownloadPdf = async function(html, fileName){
+            try {
+                const res = await fetch('/contract/generate', {
+                    method: 'POST',
+                    headers: { 'Content-Type': 'application/json' },
+                    body: JSON.stringify({ html: html, fileName: fileName })
+                });
+                if(!res.ok){
+                    throw new Error('PDF generation failed: ' + res.status);
+                }
+                const blob = await res.blob();
+                const url = URL.createObjectURL(blob);
+                const a = document.createElement('a');
+                a.href = url;
+                a.download = (fileName || 'contract') + '.pdf';
+                document.body.appendChild(a);
+                a.click();
+                a.remove();
+                setTimeout(()=>URL.revokeObjectURL(url), 5000);
+            } catch(e){
+                console.error(e);
+            }
+        };
+    </script>
     <script>
         // elementId: id نوار (مثلاً "top")
         // containerSelector: کانتینری که اسکرول می‌خوره؛ برای MudLayout معمولا ".mud-main-content"