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

skills/wordpress-theme-to-emdash/scaffold/public/favicon.svg

@@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32">
+  <rect width="32" height="32" fill="#0066cc" rx="6"/>
+  <text x="16" y="22" font-family="system-ui, sans-serif" font-size="16" font-weight="600" fill="white" text-anchor="middle">E</text>
+</svg>