feat(settings): add appearance toggle to hide the Explore tab

The Explore tab appears for every Plex-backed profile because the Plex
Discover catalog source connects implicitly, with no way to opt out
short of a Jellyfin-only profile. Add a Show Explore Tab switch to
Appearance > Navigation that hides the tab in the bottom navigation and
side rail. UI-only: catalog sources stay connected so watchlist
surfaces keep working while the tab is hidden.

close #1844

lib/i18n/da.i18n.json

@@ -323,6 +323,8 @@
     "showNavBarLabels": "Vis tekst på navigationslinjen",
     "showNavBarLabelsDescription": "Vis tekst under ikonerne på navigationslinjen",
     "startupSection": "Startsektion",
+    "showExploreTab": "",
+    "showExploreTabDescription": "",
     "liveTvDefaultFavorites": "Vis favoritkanaler som standard",
     "liveTvDefaultFavoritesDescription": "Vis kun favoritkanaler ved åbning af Live TV",
     "display": "Skærm",