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/Migrations/DatabaseModelSnapshot.cs

@@ -431,6 +431,11 @@ namespace Musify.Infrastructure.Persistence.Migrations
                     b.Property<long>("UserId")
                         .HasColumnType("bigint");
 
+                    b.Property<int>("Visibility")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("integer")
+                        .HasDefaultValue(0);
+
                     b.HasKey("Id");
 
                     b.HasIndex("UserId");
@@ -518,6 +523,31 @@ namespace Musify.Infrastructure.Persistence.Migrations
                     b.ToTable("TrackArtist");
                 });
 
+            modelBuilder.Entity("Musify.Domain.Entities.TrackLike", b =>
+                {
+                    b.Property<Guid>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("uuid");
+
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<Guid>("TrackId")
+                        .HasColumnType("uuid");
+
+                    b.Property<long>("UserId")
+                        .HasColumnType("bigint");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("TrackId");
+
+                    b.HasIndex("UserId", "TrackId")
+                        .IsUnique();
+
+                    b.ToTable("TrackLikes");
+                });
+
             modelBuilder.Entity("Musify.Domain.Entities.Upload", b =>
                 {
                     b.Property<Guid>("Id")
@@ -636,6 +666,31 @@ namespace Musify.Infrastructure.Persistence.Migrations
                     b.ToTable("User");
                 });
 
+            modelBuilder.Entity("Musify.Domain.Entities.UserFollow", b =>
+                {
+                    b.Property<Guid>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("uuid");
+
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<long>("FollowedId")
+                        .HasColumnType("bigint");
+
+                    b.Property<long>("FollowerId")
+                        .HasColumnType("bigint");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("FollowedId");
+
+                    b.HasIndex("FollowerId", "FollowedId")
+                        .IsUnique();
+
+                    b.ToTable("UserFollows");
+                });
+
             modelBuilder.Entity("Musify.Domain.Entities.UserHasTrack", b =>
                 {
                     b.Property<Guid>("Id")
@@ -1105,6 +1160,25 @@ namespace Musify.Infrastructure.Persistence.Migrations
                     b.Navigation("Track");
                 });
 
+            modelBuilder.Entity("Musify.Domain.Entities.TrackLike", b =>
+                {
+                    b.HasOne("Musify.Domain.Entities.Track", "Track")
+                        .WithMany()
+                        .HasForeignKey("TrackId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.HasOne("Musify.Domain.Entities.User", "User")
+                        .WithMany()
+                        .HasForeignKey("UserId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.Navigation("Track");
+
+                    b.Navigation("User");
+                });
+
             modelBuilder.Entity("Musify.Domain.Entities.UploadIntent", b =>
                 {
                     b.HasOne("Musify.Domain.Entities.User", "User")
@@ -1116,6 +1190,25 @@ namespace Musify.Infrastructure.Persistence.Migrations
                     b.Navigation("User");
                 });
 
+            modelBuilder.Entity("Musify.Domain.Entities.UserFollow", b =>
+                {
+                    b.HasOne("Musify.Domain.Entities.User", "Followed")
+                        .WithMany()
+                        .HasForeignKey("FollowedId")
+                        .OnDelete(DeleteBehavior.Restrict)
+                        .IsRequired();
+
+                    b.HasOne("Musify.Domain.Entities.User", "Follower")
+                        .WithMany()
+                        .HasForeignKey("FollowerId")
+                        .OnDelete(DeleteBehavior.Restrict)
+                        .IsRequired();
+
+                    b.Navigation("Followed");
+
+                    b.Navigation("Follower");
+                });
+
             modelBuilder.Entity("Musify.Domain.Entities.UserHasTrack", b =>
                 {
                     b.HasOne("Musify.Domain.Entities.Track", "Track")