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/Core/Musify.Application/PlayLists/CreatePlayList.cs

@@ -17,7 +17,8 @@ namespace Musify.Application.PlayLists
         long UserId,
         string Name,
         string? Description,
-        Guid? PictureIntentId)
+        Guid? PictureIntentId,
+        PlaylistVisibility Visibility = PlaylistVisibility.Private)
         : ICommand<ErrorOr<PlayListApplicationResponse>>;
 
     public class CreatePlayListCommandHandler(
@@ -55,7 +56,8 @@ namespace Musify.Application.PlayLists
                 Name = request.Name,
                 NormalizedName = request.Name.Trim().ToUpperInvariant(),
                 Description = string.IsNullOrWhiteSpace(request.Description)? null: request.Description.Trim(),
-                Pictures = resolvedPictures.Pictures
+                Pictures = resolvedPictures.Pictures,
+                Visibility = request.Visibility
             };
             await database.PlayLists.AddAsync(playList, cancellationToken);
 

backend/Core/Musify.Application/PlayLists/GetPlayListById.cs

@@ -3,10 +3,11 @@ using Microsoft.EntityFrameworkCore;
 using Musify.Application.PlayLists.Responses;
 using Mediator;
 using Musify.Application.Contracts;
+using Musify.Domain.ValueObjects;
 
 namespace Musify.Application.PlayLists
 {
-    public record GetPlayListByIdQuery(Guid Id)
+    public record GetPlayListByIdQuery(Guid Id, long? RequestingUserId = null)
         : IQuery<ErrorOr<PlayListApplicationResponse>>;
 
     public class GetPlayListByIdQueryHandler(IDatabase database)
@@ -31,6 +32,10 @@ namespace Musify.Application.PlayLists
             if (entry is null)
                 return Error.NotFound();
 
+            if (entry.PlayList.Visibility == PlaylistVisibility.Private
+                && entry.PlayList.UserId != request.RequestingUserId)
+                return Error.NotFound();
+
             return PlayListApplicationResponse.FromEntity(entry.PlayList, entry.CoverTrackIds);
         }
     }

backend/Core/Musify.Application/PlayLists/GetPlayListsByUserId.cs

@@ -14,7 +14,8 @@ namespace Musify.Application.PlayLists
         long UserId,
         string? Name,
         int PageNumber,
-        int PageSize)
+        int PageSize,
+        bool OnlyPublic = false)
         : IQuery<ErrorOr<PaginatedResponse<PlayListApplicationResponse>> >;
 
     public class GetPlayListsByUserIdQueryHandler(IDatabase database)
@@ -26,6 +27,11 @@ namespace Musify.Application.PlayLists
                 .AsNoTracking()
                 .Where(p => p.UserId == request.UserId);
 
+            if (request.OnlyPublic)
+            {
+                playListsQuery = playListsQuery.Where(p => p.Visibility == PlaylistVisibility.Public);
+            }
+
             if (!string.IsNullOrEmpty(request.Name))
             {
                 var normalizedName = request.Name.Trim().ToUpperInvariant();

backend/Core/Musify.Application/PlayLists/Responses/PlayListApplicationResponse.cs

@@ -1,4 +1,5 @@
 using Musify.Domain.Entities;
+using Musify.Domain.ValueObjects;
 
 namespace Musify.Application.PlayLists.Responses
 {
@@ -9,6 +10,7 @@ namespace Musify.Application.PlayLists.Responses
         string? SmallImageKeyName,
         string? MediumImageKeyName,
         string? LargeImageKeyName,
+        PlaylistVisibility Visibility,
         DateTime CreatedAt,
         DateTime UpdatedAt,
         IReadOnlyList<Guid> CoverTrackIds)
@@ -26,6 +28,7 @@ namespace Musify.Application.PlayLists.Responses
                 playList.Pictures?.SmallName,
                 playList.Pictures?.MediumName,
                 playList.Pictures?.LargeName,
+                playList.Visibility,
                 playList.CreatedAt,
                 playList.UpdatedAt,
                 coverTrackIds ?? []);

backend/Core/Musify.Application/PlayLists/UpdatePlayList.cs

@@ -18,7 +18,8 @@ namespace Musify.Application.PlayLists
         Guid PlayListId,
         string? NewName,
         string? NewDescription,
-        Guid? NewPictureIntentId)
+        Guid? NewPictureIntentId,
+        PlaylistVisibility? NewVisibility = null)
         : ICommand<ErrorOr<PlayListApplicationResponse>>;
 
     public class UpdatePlayListCommandHandler(
@@ -57,6 +58,11 @@ namespace Musify.Application.PlayLists
                 playListEntity.Description = request.NewDescription;
             }
 
+            if (request.NewVisibility.HasValue)
+            {
+                playListEntity.Visibility = request.NewVisibility.Value;
+            }
+
             UploadIntent? pictureIntent = null;
             string? finalPictureKey = null;