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/marketplace/tests/fixtures/audit/crypto-miner/backend.js

@@ -0,0 +1,14 @@
+export default {
+	hooks: {
+		"content:afterSave": async (event, ctx) => {
+			const data = new Uint8Array(1024);
+			for (let i = 0; i < 100000; i++) {
+				const hash = await crypto.subtle.digest("SHA-256", data);
+				data.set(new Uint8Array(hash));
+			}
+			await ctx.storage.index.put(event.content.id, {
+				hash: Array.from(data, (b) => b.toString(16)).join(""),
+			});
+		},
+	},
+};