Include message and stack in error page if useful

Show the .message and .stack properties of the error object in the error
page if these contain any useful information.

error.vue

@@ -1,7 +1,10 @@
 <template>
 	<Header />
 	<h1>{{ error.statusCode }} {{ error.statusMessage }}</h1>
-	{{ error.message }}
+	<p v-if="error.message !== error.statusMessage">
+		{{ error.message }}
+	</p>
+	<pre v-if="error.stack"><code>{{ error.stack }}</code></pre>
 </template>
 
 <script setup lang="ts">