Include error message text on page

Also remove the '500' h1 from the error

Closes #3248

.eslintrc.cjs

@@ -50,7 +50,7 @@ module.exports = {
         },
     ],
     env: { browser: true, es2020: true },
-    ignorePatterns: ["backend_proto.d.ts", "*.svelte.d.ts", "vendor", "extra/*", "vite.config.ts"],
+    ignorePatterns: ["backend_proto.d.ts", "*.svelte.d.ts", "vendor", "extra/*", "vite.config.ts", "hooks.client.js"],
     globals: {
         globalThis: false,
         NodeListOf: false,

ts/routes/+error.svelte

@@ -0,0 +1,11 @@
+<!--
+Copyright: Ankitects Pty Ltd and contributors
+License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
+-->
+<script lang="ts">
+    import { page } from "$app/stores";
+
+    $: message = $page.error!.message;
+</script>
+
+{message}

ts/src/hooks.client.js

@@ -0,0 +1,8 @@
+/** @type {import('@sveltejs/kit').HandleClientError} */
+export async function handleError({ error, event, status, message }) {
+    /** @type {any} */
+    const anyError = error;
+    return {
+        message: anyError.message,
+    };
+}