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.Infrastructure/Persistence/Database.cs

@@ -2,6 +2,7 @@ using Microsoft.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore.Storage;
 using MassTransit;
 using Musify.Domain.Entities;
+using Musify.Domain.ValueObjects;
 using Musify.Infrastructure.Configuration;
 using Musify.Infrastructure.MassTransit.Sagas;
 using AppIDatabase = Musify.Application.Contracts.IDatabase;
@@ -88,6 +89,10 @@ namespace Musify.Infrastructure.Persistence
                 .HasIndex(artist => artist.ExternalId)
                 .IsUnique();
 
+            modelBuilder.Entity<PlayList>()
+                .Property(playList => playList.Visibility)
+                .HasDefaultValue(PlaylistVisibility.Private);
+
             modelBuilder.Entity<PlayList>()
                 .OwnsOne(playList => playList.Pictures, pictures =>
                 {
@@ -159,6 +164,26 @@ namespace Musify.Infrastructure.Persistence
             modelBuilder.Entity<MixItem>()
                 .HasIndex(item => new { item.MixId, item.Position });
 
+            modelBuilder.Entity<TrackLike>()
+                .HasIndex(like => new { like.UserId, like.TrackId })
+                .IsUnique();
+
+            modelBuilder.Entity<UserFollow>()
+                .HasOne(follow => follow.Follower)
+                .WithMany()
+                .HasForeignKey(follow => follow.FollowerId)
+                .OnDelete(DeleteBehavior.Restrict);
+
+            modelBuilder.Entity<UserFollow>()
+                .HasOne(follow => follow.Followed)
+                .WithMany()
+                .HasForeignKey(follow => follow.FollowedId)
+                .OnDelete(DeleteBehavior.Restrict);
+
+            modelBuilder.Entity<UserFollow>()
+                .HasIndex(follow => new { follow.FollowerId, follow.FollowedId })
+                .IsUnique();
+
             var playListProcessing = modelBuilder.Entity<PlayListProcessingState>();
             playListProcessing.HasKey(state => state.CorrelationId);
             playListProcessing.Property(state => state.CorrelationId).ValueGeneratedNever();
@@ -206,6 +231,10 @@ namespace Musify.Infrastructure.Persistence
 
         public DbSet<ListeningHistory> ListeningHistories => Set<ListeningHistory>();
 
+        public DbSet<TrackLike> TrackLikes => Set<TrackLike>();
+
+        public DbSet<UserFollow> UserFollows => Set<UserFollow>();
+
         public async Task<IDatabaseTransaction> BeginTransactionAsync(System.Data.IsolationLevel isolationLevel, CancellationToken cancellationToken)
         {
             var transaction = await Database.BeginTransactionAsync(isolationLevel, cancellationToken);