feat: add error handling to job editor and Error page

Wrap job editor initialization in try/catch to display errors instead of
crashing the circuit. Make LoadSavedResults async. Add a simple Error
page for the production exception handler.

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

CutList.Web/Components/Pages/Error.razor

@@ -0,0 +1,17 @@
+@page "/Error"
+
+<PageTitle>Error</PageTitle>
+
+<div class="container mt-5">
+    <div class="row justify-content-center">
+        <div class="col-md-8">
+            <div class="card border-danger">
+                <div class="card-body text-center">
+                    <h1 class="text-danger mb-3">Something went wrong</h1>
+                    <p class="lead">An unexpected error occurred. Please try again later.</p>
+                    <a href="/" class="btn btn-primary mt-3">Return to home page</a>
+                </div>
+            </div>
+        </div>
+    </div>
+</div>