Show popular fetch phases in nav indicator and Downloads page

- Phase 1 (crawling) now creates the task immediately so Downloads shows it
- Phase label updates to 'Enriching view counts' when phase 2 starts
- Nav bar DownloadIndicator also polls /channels/tasks and shows spinning
  indicator + progress % for background tasks (not just file downloads)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/Downloads.jsx

@@ -141,9 +141,12 @@ export default function DownloadsPage() {
               const pct = task.total > 0 ? (task.done / task.total) * 100 : 0;
               return (
                 <div key={task.id} className="bg-zinc-900 rounded-xl p-4">
+                  <p className="text-sm font-medium text-zinc-100 mb-0.5">{task.label}</p>
                   <div className="flex items-center justify-between mb-1">
-                    <p className="text-sm font-medium text-zinc-100">{task.label}</p>
-                    <span className="text-xs text-zinc-400 tabular-nums">{task.done}/{task.total}</span>
+                    <span className="text-xs text-zinc-400">{task.phase || "Running…"}</span>
+                    {task.total > 0 && (
+                      <span className="text-xs text-zinc-400 tabular-nums">{task.done}/{task.total}</span>
+                    )}
                   </div>
                   <ProgressBar pct={pct} />
                 </div>