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/worker.ts

@@ -0,0 +1,5 @@
+import handler from "@astrojs/cloudflare/entrypoints/server";
+
+export { PluginBridge } from "@emdash-cms/cloudflare/sandbox";
+
+export default handler;