Truncate noisy build-failure output, fix the recurring terrain death

The web UI was showing a raw ~500k-character stdout/stderr dump on a
failed build — go-pmtiles' extract logs one progress line per chunk,
which is fine on a terminal (it overwrites itself) but not captured
non-interactively. command_output now keeps just the tail, and the
status line renders it with preserved line breaks in a scrollable box
instead of one unreadable blob.

Root cause of the actual failure (terrain build dying ~11 minutes in
with an HTTP/2 stream reset): go-pmtiles' default --overfetch=0.05
merged this multi-country planet.pmtiles extract into a single ~60GB
request with no way to resume after a dropped stream. --overfetch=0
splits it into many smaller requests instead.

public/css/style.css

@@ -542,6 +542,14 @@ html, body {
   font-size: 12px;
 }
 
+.offline-data-panel__status--error {
+  white-space: pre-wrap;
+  word-break: break-word;
+  max-height: 200px;
+  overflow-y: auto;
+  color: #b3261e;
+}
+
 .offline-data-panel__update-badge {
   color: #b8860b;
 }