Add likes, follows and playlist visibility; redesign web-player UI

Backend:
- New Likes feature (toggle/get liked tracks) and endpoints
- User follow/unfollow, listening stats, public user profile
- Playlist visibility (public/private) support
- Various auth and DTO/response adjustments to support the above

Frontend (web-player):
- New design system pass: theme tokens/mode (light/dark), glass menu,
  tabs bar, player dock/extras/queue components, mix tiles, artist link
- New routes: Liked, public user profile (/u/[id]), likes API proxy
- Search refactor: shared SearchBox component used by TopBar and
  MobileHeader (search now reachable on mobile), live results as you
  type instead of requiring Enter, dropped the "Buscando…" quick-result
  preview
- Removed now-unused components (MobileNav, CoverBadge, MixBentoTile,
  PlayPauseOverlay, SuggestionsTable, userDirectory)
- Design handoff reference docs added under web-player/design_handoff_musify_player
  and web-player/docs/design-system-refactor-plan.md

backend/Hosts/Musify.Api/OpenApi/OpenApiOptionsSetup.cs

@@ -3,6 +3,7 @@ using Microsoft.AspNetCore.OpenApi;
 using Microsoft.Extensions.Options;
 using Microsoft.OpenApi;
 using Musify.Api.Authentication;
+using Musify.Application.Serialization;
 
 namespace Musify.Api.OpenApi;
 
@@ -38,6 +39,24 @@ public sealed class OpenApiOptionsSetup(IOptions<AuthenticationConfiguration> op
             return Task.CompletedTask;
         } );
 
+        // Properties annotated with [JsonConverter(typeof(LongAsStringConverter))] (id-shaped
+        // `long` fields — see that converter for why) serialize as a JSON string, but the
+        // schema generator still reflects the declared CLR `long`/`long?` type as a bare
+        // int64 number. Reconcile the declared schema so generated clients (openapi-typescript)
+        // type exactly those properties as `string`, matching what actually goes over the wire —
+        // scoped to the attribute, not the CLR type, so unrelated `long` fields (byte sizes, …)
+        // are left alone.
+        options.AddSchemaTransformer((schema, context, _) =>
+        {
+            if (context.JsonPropertyInfo?.CustomConverter is LongAsStringConverter or NullableLongAsStringConverter)
+            {
+                schema.Type = JsonSchemaType.String;
+                schema.Format = null;
+            }
+
+            return Task.CompletedTask;
+        } );
+
         options.AddOperationTransformer((operation, context, _) =>
         {
             var requiresAuthorization = context.Description.ActionDescriptor.EndpointMetadata