fix(podcasts): page-load polls during downloads; indeterminate bar slides

A fresh detail-page load while downloads were active rendered the
NON-polling episode container (PollingEpisodeList was only reachable
via the /episodes partial route after Refresh), so the page froze
until the user refreshed manually. PodcastDetailPage now picks the
variant the same way the route does — HasActiveDownloads selects the
every-2s poll container.

Also: the indeterminate progress bar (feeds without Content-Length,
e.g. Scribl) used animate-pulse, which fades in place and reads as
frozen; replaced with a sliding shimmer keyframe
(.podcast-progress-indeterminate, 33% sliver, translating -100% ->
300%) in input.css. The live MB counter stays.

§0 item 1.

web/static/input.css

@@ -2127,3 +2127,17 @@
   border-color: var(--status-danger) !important;
 }
 
+/* ---------- Podcast download indeterminate bar (sliding shimmer) ----------
+   Podcast feeds without Content-Length (e.g. Scribl) get an
+   indeterminate progress bar; animate-pulse fades in place and looks
+   frozen to the user, so a sliver slides across instead (2026-10-30,
+   §0 item 1). */
+@keyframes podcast-indeterminate {
+  from { transform: translateX(-100%); }
+  to { transform: translateX(300%); }
+}
+.podcast-progress-indeterminate > div {
+  width: 33.33%;
+  animation: podcast-indeterminate 1.3s ease-in-out infinite;
+}
+