feat(library): genre sliders, artist links, and navigation utils

- music landing: diverse per-genre album sliders (online counts /
  offline wide-probe fallback) and home-screen library shortcuts
- add ArtistLinks component and shared navigation/genreDiversity utils
- player/playback-mode refinements across Rust and frontend

src/routes/library/movies/+page.svelte

@@ -2,6 +2,7 @@
 <script lang="ts">
   import { onMount } from "svelte";
   import { goto } from "$app/navigation";
+  import { navigateBack } from "$lib/utils/navigation";
   import { currentLibrary } from "$lib/stores/library";
   import { movies } from "$lib/stores/movies";
   import { isServerReachable } from "$lib/stores/connectivity";
@@ -85,7 +86,7 @@
     <div class="flex items-center justify-between px-4">
       <h1 class="text-3xl font-bold text-white">{$currentLibrary?.name ?? "Movies"}</h1>
       <button
-        onclick={() => goto("/library")}
+        onclick={() => navigateBack("/library")}
         class="p-2 rounded-lg hover:bg-white/10 transition-colors text-gray-400 hover:text-white"
         title="Back to libraries"
         aria-label="Back to libraries"