fix(delete): prune in-memory SerieList cache after delete

delete_series() removed the row from the database and the folder
from disk, but never evicted the entry from SerieList.keyDict — the
in-memory cache that list_series_with_filters() reads from via
SeriesApp.list.GetList(). As a result /api/anime kept returning the
deleted series on every page reload (the 'Beyblade Burst still listed
after delete' bug).

Changes:
* Add SerieList.remove(key) so the cache has a proper eviction API.
* In delete_series(), call it (or fall back to keyDict.pop) after a
  successful DB delete.
* Broadcast a broader series_list_changed event so any client that
  missed the specific series_deleted event can re-sync by re-fetching
  /api/anime. Front-end: new SERIES_LIST_CHANGED constant, handler
  that triggers SeriesManager.reloadSeries().
* Two new regression tests: one asserting the in-memory cache is
  pruned, one asserting the broader broadcast fires.

src/server/web/static/js/index/series-manager.js

@@ -584,6 +584,17 @@ AniWorld.SeriesManager = (function() {
         }
     }
 
+    /**
+     * Re-fetch the series list from the server. Used as a durable
+     * backstop when receiving the broader series_list_changed WS event
+     * so local state cannot drift from the server's in-memory cache.
+     * @returns {Promise<void>}
+     */
+    function reloadSeries() {
+        console.info('[SeriesManager] Reloading series from server');
+        return loadSeries();
+    }
+
     // Public API
     return {
         init: init,
@@ -596,6 +607,7 @@ AniWorld.SeriesManager = (function() {
         updateSeriesLoadingStatus: updateSeriesLoadingStatus,
         updateSingleSeries: updateSingleSeries,
         updateSeriesKey: updateSeriesKey,
-        removeSeries: removeSeries
+        removeSeries: removeSeries,
+        reloadSeries: reloadSeries
     };
 })();