fix(programa): use is:global for filter CSS to cross Astro component scope

The 'only favourites' filter was toggling the button state and
adding the .filter-favorites-only class to the list view, but the
session cards were not being hidden. Reason: the CSS rule was in
ProgramaPage.astro and Astro's scoped styles injected
data-astro-cid-nm3rvpko into every selector, including .schedule-list
and li. But those elements are rendered by ScheduleList.astro which
has its own data-astro-cid-zmszfzov, so the selector never matched.

Fix: extract the filter CSS into an is:global block so the selector
reaches across the component boundary. Verified end-to-end with
Playwright:
- 0 favourites: 56/56 hidden (everything is filtered out)
- 1 favourite set: 1 visible, 55 hidden
- Toggle off: 56 visible again

Author: itziarZG

src/components/ProgramaPage.astro

@@ -143,6 +143,14 @@ const schedule = await getSchedule()
   .schedule-view.hidden {
     display: none;
   }
+</style>
+
+<style is:global>
+  /* Hide non-favourite session cards when the favourites filter is on.
+     The .schedule-list and its <li> children are rendered by
+     ScheduleList.astro (its own Astro scope, data-astro-cid-zmszfzov),
+     so we use is:global here to let this rule reach across component
+     boundaries. */
   #schedule-list-view.filter-favorites-only .schedule-list li:not(.is-favorite) {
     display: none;
   }