fix(dashboard): hold the hero skeleton for a live candidate's first programme

A live hero slide exists only once its channel has a programme on air.
With a live favorite as the only candidate, the skeleton went away when
history, favorites and recently added had loaded, and the live slide was
inserted when the portal or XMLTV answer arrived, shifting the rails.

DashboardLiveEpgPresenter now reports while a hero candidate awaits its
first portal or XMLTV answer, and the hero keeps its skeleton for that,
at most 2 s from its creation. Once the skeleton has gone it does not
come back.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/architecture/workspace-dashboard.md

@@ -76,9 +76,12 @@ Render rules:
 3. The hero (`lib-dashboard-hero`) renders when it has at least one slide;
    see [Cinematic Hero](#cinematic-hero). It shows its own skeleton while
    it has no slide and any of its sources (history, favorites, Xtream
-   recently added) is still on its first load; dropping it earlier removed
-   the hero and inserted it again when a later source featured a title,
-   moving every rail below twice. An item enters recent history only after
+   recently added) is still on its first load, or a live candidate still
+   waits for its first programme answer (portal or XMLTV, for at most
+   `DASHBOARD_HERO_LIVE_ANSWER_WAIT_MS`, 2 s, from the hero's creation).
+   Dropping it earlier removed the hero and inserted it again when a later
+   source featured a title, moving every rail below twice. Once the
+   skeleton has gone it does not come back. An item enters recent history only after
    its stream has really played (see "Recently Viewed Confirmation" in
    `embedded-inline-playback.md`), so a channel that failed at once never
    becomes a hero slide.