Emdash source with visual editor image upload fix

Fixes:
1. media.ts: wrap placeholder generation in try-catch
2. toolbar.ts: check r.ok, display error message in popover

templates/blog-cloudflare/src/pages/404.astro

@@ -0,0 +1,33 @@
+---
+import Base from "../layouts/Base.astro";
+---
+
+<Base title="Page not found">
+	<div class="not-found">
+		<h1>404</h1>
+		<p>The page you're looking for doesn't exist.</p>
+		<a href="/">Go back home</a>
+	</div>
+</Base>
+
+<style>
+	.not-found {
+		text-align: center;
+		padding: var(--spacing-24) var(--spacing-6);
+	}
+
+	.not-found h1 {
+		font-size: var(--font-size-5xl);
+		margin-bottom: var(--spacing-2);
+		color: var(--color-border);
+	}
+
+	.not-found p {
+		color: var(--color-muted);
+		margin-bottom: var(--spacing-6);
+	}
+
+	.not-found a {
+		color: var(--color-text);
+	}
+</style>