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/playground/src/worker.ts

@@ -0,0 +1,14 @@
+/**
+ * Playground Worker Entrypoint
+ *
+ * Exports:
+ * - default: Astro handler
+ * - EmDashPreviewDB: Durable Object class for playground databases
+ */
+
+import handler from "@astrojs/cloudflare/entrypoints/server";
+
+// Export the DO class so Cloudflare can instantiate it
+export { EmDashPreviewDB } from "@emdash-cms/cloudflare/db/playground";
+
+export default handler;