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

demos/preview/astro.config.mjs

@@ -0,0 +1,34 @@
+import cloudflare from "@astrojs/cloudflare";
+import react from "@astrojs/react";
+import { previewDatabase } from "@emdash-cms/cloudflare";
+import { defineConfig, fontProviders } from "astro/config";
+import emdash from "emdash/astro";
+
+export default defineConfig({
+	output: "server",
+	adapter: cloudflare(),
+	integrations: [
+		react(),
+		emdash({
+			// DO-backed preview database — populated from source site snapshots
+			database: previewDatabase({ binding: "PREVIEW_DB" }),
+		}),
+	],
+	fonts: [
+		{
+			provider: fontProviders.google(),
+			name: "Inter",
+			cssVariable: "--font-sans",
+			weights: [400, 500, 600, 700],
+			fallbacks: ["sans-serif"],
+		},
+		{
+			provider: fontProviders.google(),
+			name: "JetBrains Mono",
+			cssVariable: "--font-mono",
+			weights: [400, 500],
+			fallbacks: ["monospace"],
+		},
+	],
+	devToolbar: { enabled: false },
+});