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

scripts/query-counts.snapshot.d1.json

@@ -0,0 +1,18 @@
+{
+	"GET / (cold)": 21,
+	"GET / (warm)": 11,
+	"GET /category/development (cold)": 25,
+	"GET /category/development (warm)": 14,
+	"GET /pages/about (cold)": 20,
+	"GET /pages/about (warm)": 10,
+	"GET /posts (cold)": 21,
+	"GET /posts (warm)": 11,
+	"GET /posts/building-for-the-long-term (cold)": 32,
+	"GET /posts/building-for-the-long-term (warm)": 22,
+	"GET /rss.xml (cold)": 13,
+	"GET /rss.xml (warm)": 4,
+	"GET /search (cold)": 22,
+	"GET /search (warm)": 12,
+	"GET /tag/webdev (cold)": 25,
+	"GET /tag/webdev (warm)": 14
+}