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.

tests/unit/test_delete_anime_service.py

@@ -646,6 +646,111 @@ class TestDeleteSeriesService:
         db_delete_mock.assert_not_called()
         assert result.success is False
 
+    # ------------------------------------------------------------------
+    # In-memory keyDict cache eviction
+    # ------------------------------------------------------------------
+
+    @pytest.mark.asyncio
+    async def test_delete_series_evicts_in_memory_cache(
+        self, anime_service, mock_series_app
+    ):
+        """After a successful DB delete, the in-memory SerieList.keyDict
+        entry for that series must be removed.
+
+        The /api/anime list endpoint reads from SeriesApp.list.keyDict
+        via list_series_with_filters(). If the cache is not pruned, the
+        deleted series keeps appearing in the listing on every page
+        reload — exactly the Beyblade Burst bug.
+        """
+        from src.server.database.SerieList import SerieList
+
+        mock_session = AsyncMock()
+        mock_ctx = _make_db_ctx(mock_session)
+
+        mock_series = MagicMock()
+        mock_series.key = "beyblade-burst-rise"
+        mock_series.name = "Beyblade Burst Rise"
+        mock_series.folder = "Beyblade Burst Rise (2016)"
+        mock_series.id = 487
+
+        # Use a real SerieList instance — the same type the production
+        # code mutates — so the eviction actually exercises the real
+        # remove() method (a MagicMock would just return more mocks).
+        real_list = SerieList(str(mock_series_app.directory_to_search))
+        real_list.keyDict["beyblade-burst-rise"] = mock_series
+        mock_series_app.list = real_list
+
+        anime_service._websocket_service = MagicMock()
+        anime_service._websocket_service.broadcast_series_deleted = AsyncMock()
+        anime_service._websocket_service.broadcast_series_list_changed = AsyncMock()
+
+        with patch(
+            "src.server.database.connection.get_db_session",
+            return_value=mock_ctx,
+        ), patch(
+            "src.server.database.service.AnimeSeriesService.get_by_key",
+            new_callable=AsyncMock,
+            return_value=mock_series,
+        ), patch(
+            "src.server.database.service.AnimeSeriesService.delete",
+            new_callable=AsyncMock,
+            return_value=True,
+        ):
+            result = await anime_service.delete_series(
+                key="beyblade-burst-rise",
+                delete_database=True,
+                delete_folder=False,
+            )
+
+        assert result.success is True
+        assert "beyblade-burst-rise" not in real_list.keyDict, (
+            "In-memory cache still contains the deleted series — "
+            "/api/anime will keep returning it after a page reload"
+        )
+
+    @pytest.mark.asyncio
+    async def test_delete_series_broadcasts_series_list_changed(
+        self, anime_service, mock_series_app
+    ):
+        """A stronger ``series_list_changed`` broadcast fires after delete
+        so any connected client can re-sync without relying on the more
+        specific ``series_deleted`` event reaching them.
+        """
+        mock_session = AsyncMock()
+        mock_ctx = _make_db_ctx(mock_session)
+
+        mock_series = MagicMock()
+        mock_series.key = "test-key"
+        mock_series.name = "Test Series"
+        mock_series.folder = "Test Series (2023)"
+        mock_series.id = 1
+
+        mock_series_app.list.keyDict = {"test-key": mock_series}
+
+        anime_service._websocket_service = MagicMock()
+        anime_service._websocket_service.broadcast_series_deleted = AsyncMock()
+        anime_service._websocket_service.broadcast_series_list_changed = AsyncMock()
+
+        with patch(
+            "src.server.database.connection.get_db_session",
+            return_value=mock_ctx,
+        ), patch(
+            "src.server.database.service.AnimeSeriesService.get_by_key",
+            new_callable=AsyncMock,
+            return_value=mock_series,
+        ), patch(
+            "src.server.database.service.AnimeSeriesService.delete",
+            new_callable=AsyncMock,
+            return_value=True,
+        ):
+            await anime_service.delete_series(
+                key="test-key",
+                delete_database=True,
+                delete_folder=False,
+            )
+
+        anime_service._websocket_service.broadcast_series_list_changed.assert_called_once()
+
     # ------------------------------------------------------------------
     # Orphan folder recovery (DB row gone, folder still on disk)
     # ------------------------------------------------------------------