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

packages/blocks/tsdown.config.ts

@@ -0,0 +1,10 @@
+import { defineConfig } from "tsdown";
+
+export default defineConfig({
+	entry: ["src/index.ts", "src/server.ts"],
+	format: ["esm"],
+	dts: true,
+	clean: true,
+	platform: "browser",
+	external: ["react", "react-dom", "react/jsx-runtime", "react/jsx-dev-runtime"],
+});