feat(playlists): total playtime in header + sticky-header fade fix (E9 S1)

Surface the playlist's total playtime beside the item count in the detail
header (12D) — sums every item's duration (formatRuntime "h m", matching the
approved mockup), hidden when nothing sums. Data is already client-side; no
backend change.

Pass fadeTop:false for the playlists page (12B) so the shell's top edge-fade
no longer sits over the already-sticky column header (tableHeader.tsx:257),
matching the channels/audit pages.

frontend/src/components/moduleRegistry.tsx

@@ -94,7 +94,7 @@ export type PageDef = {
 export const PAGE_CONTENT: Record<Page, PageDef> = {
   feed: { Component: FeedPage },
   channels: { Component: Channels, fadeTop: false, maxWidth: "96rem" },
-  playlists: { Component: Playlists, maxWidth: "64rem" },
+  playlists: { Component: Playlists, fadeTop: false, maxWidth: "64rem" },
   plex: { Component: PlexBrowse, maxWidth: "1600px" },
   notifications: { Component: NotificationsPanel, maxWidth: "48rem" },
   messages: { Component: MessagesPage },