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/hate-imagery/manifest.json

@@ -0,0 +1,10 @@
+{
+	"id": "wallpaper-plugin",
+	"version": "1.0.0",
+	"capabilities": ["read:content"],
+	"allowedHosts": [],
+	"storage": {},
+	"hooks": [],
+	"routes": [],
+	"admin": {}
+}