Replace String.to_integer with safe Integer.parse

Use Integer.parse/1 instead of String.to_integer/1 on user-supplied
and external API input to prevent ArgumentError crashes on non-numeric
values. Adds fallback defaults or nil returns at each call site.

lib/music_library_web/live/scrobble_live/show.ex

@@ -162,7 +162,7 @@ defmodule MusicLibraryWeb.ScrobbleLive.Show do
   end
 
   def handle_event("scrobble_medium", %{"medium_number" => number}, socket) do
-    number = String.to_integer(number)
+    {number, ""} = Integer.parse(number)
 
     case ScrobbleActivity.scrobble_medium(number, socket.assigns.release,
            finished_at: DateTime.utc_now()