Remove comments from backend and web-player source

Strip //, /* */ and XML doc comments from all backend .cs files, and
JS/TS/CSS/HTML comments from web-player source (.ts, .svelte, .css),
per the project's no-comments convention.

backend/Core/Musify.Application/Mixes/MixItemMapper.cs

@@ -5,9 +5,7 @@ using Musify.Domain.Entities;
 
 namespace Musify.Application.Mixes
 {
-    /// <summary>Resolves MixItem rows to their MixItemApplicationResponse shape via a single batched
-    /// track lookup, instead of an EF Include chain deep enough (Mix -&gt; Items -&gt; Track -&gt; Owner) to
-    /// force a correlated-subquery translation some providers (SQLite, notably) can't produce.</summary>
+
     internal static class MixItemMapper
     {
         public static async Task<List<MixItemApplicationResponse>> ToResponsesAsync(