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/Tests/Musify.Application.Tests/PlayLists/CreatePlayListCommandHandlerTests.cs

@@ -60,6 +60,34 @@ namespace Musify.Application.Tests.PlayLists
             await eventBus.Received(1).PublishAsync(Arg.Any<Musify.Application.Events.CreatePlayListResourcesEvent>(), Arg.Any<CancellationToken>());
         }
 
+        [Fact]
+        public async Task Handle_NoVisibilitySpecified_DefaultsToPrivate()
+        {
+            var user = TestEntities.User();
+            await SeedAsync(user);
+
+            var command = new CreatePlayListCommand(user.Id, "My Playlist", null, PictureIntentId: null);
+
+            var result = await CreateHandler().Handle(command, TestContext.Current.CancellationToken);
+
+            Assert.False(result.IsError);
+            Assert.Equal(Musify.Domain.ValueObjects.PlaylistVisibility.Private, result.Value.Visibility);
+        }
+
+        [Fact]
+        public async Task Handle_PublicVisibility_PersistsIt()
+        {
+            var user = TestEntities.User();
+            await SeedAsync(user);
+
+            var command = new CreatePlayListCommand(user.Id, "My Playlist", null, PictureIntentId: null, Visibility: Musify.Domain.ValueObjects.PlaylistVisibility.Public);
+
+            var result = await CreateHandler().Handle(command, TestContext.Current.CancellationToken);
+
+            Assert.False(result.IsError);
+            Assert.Equal(Musify.Domain.ValueObjects.PlaylistVisibility.Public, result.Value.Visibility);
+        }
+
         [Fact]
         public async Task Handle_UserMissing_ReturnsNotFound()
         {

backend/Tests/Musify.Application.Tests/PlayLists/GetPlayListByIdQueryHandlerTests.cs

@@ -14,7 +14,7 @@ namespace Musify.Application.Tests.PlayLists
         public async Task Handle_ExistingPlayList_ReturnsItWithCoverTrackIds()
         {
             var owner = TestEntities.User();
-            var playList = TestEntities.PlayList(owner.Id);
+            var playList = TestEntities.PlayList(owner.Id, visibility: Musify.Domain.ValueObjects.PlaylistVisibility.Public);
             var track = TestEntities.LocalTrack(owner);
             await SeedAsync(owner, playList, track, new PlayListHasTrack { PlayListId = playList.Id, TrackId = track.Id, Position = 0 });
 
@@ -32,5 +32,54 @@ namespace Musify.Application.Tests.PlayLists
 
             Assert.Equal(ErrorType.NotFound, result.FirstError.Type);
         }
+
+        [Fact]
+        public async Task Handle_PrivatePlayList_RequestedByOwner_ReturnsIt()
+        {
+            var owner = TestEntities.User();
+            var playList = TestEntities.PlayList(owner.Id, visibility: Musify.Domain.ValueObjects.PlaylistVisibility.Private);
+            await SeedAsync(owner, playList);
+
+            var result = await CreateHandler().Handle(new GetPlayListByIdQuery(playList.Id, owner.Id), TestContext.Current.CancellationToken);
+
+            Assert.False(result.IsError);
+        }
+
+        [Fact]
+        public async Task Handle_PrivatePlayList_RequestedByStranger_ReturnsNotFound()
+        {
+            var owner = TestEntities.User(1, "owner");
+            var stranger = TestEntities.User(2, "stranger");
+            var playList = TestEntities.PlayList(owner.Id, visibility: Musify.Domain.ValueObjects.PlaylistVisibility.Private);
+            await SeedAsync(owner, stranger, playList);
+
+            var result = await CreateHandler().Handle(new GetPlayListByIdQuery(playList.Id, stranger.Id), TestContext.Current.CancellationToken);
+
+            Assert.Equal(ErrorType.NotFound, result.FirstError.Type);
+        }
+
+        [Fact]
+        public async Task Handle_PrivatePlayList_RequestedAnonymously_ReturnsNotFound()
+        {
+            var owner = TestEntities.User();
+            var playList = TestEntities.PlayList(owner.Id, visibility: Musify.Domain.ValueObjects.PlaylistVisibility.Private);
+            await SeedAsync(owner, playList);
+
+            var result = await CreateHandler().Handle(new GetPlayListByIdQuery(playList.Id, RequestingUserId: null), TestContext.Current.CancellationToken);
+
+            Assert.Equal(ErrorType.NotFound, result.FirstError.Type);
+        }
+
+        [Fact]
+        public async Task Handle_PublicPlayList_RequestedAnonymously_ReturnsIt()
+        {
+            var owner = TestEntities.User();
+            var playList = TestEntities.PlayList(owner.Id, visibility: Musify.Domain.ValueObjects.PlaylistVisibility.Public);
+            await SeedAsync(owner, playList);
+
+            var result = await CreateHandler().Handle(new GetPlayListByIdQuery(playList.Id, RequestingUserId: null), TestContext.Current.CancellationToken);
+
+            Assert.False(result.IsError);
+        }
     }
 }

backend/Tests/Musify.Application.Tests/PlayLists/GetPlayListsByUserIdQueryHandlerTests.cs

@@ -27,6 +27,22 @@ namespace Musify.Application.Tests.PlayLists
             Assert.Equal("Mine", playList.Name);
         }
 
+        [Fact]
+        public async Task Handle_OnlyPublic_ReturnsOnlyPublicPlayLists()
+        {
+            var owner = TestEntities.User();
+            await SeedAsync(
+                owner,
+                TestEntities.PlayList(owner.Id, "Public one", visibility: PlaylistVisibility.Public),
+                TestEntities.PlayList(owner.Id, "Private one", visibility: PlaylistVisibility.Private));
+
+            var result = await CreateHandler().Handle(new GetPlayListsByUserIdQuery(owner.Id, Name: null, PageNumber: 1, PageSize: 10, OnlyPublic: true), TestContext.Current.CancellationToken);
+
+            Assert.False(result.IsError);
+            var playList = Assert.Single(result.Value.Items);
+            Assert.Equal("Public one", playList.Name);
+        }
+
         [Fact]
         public async Task Handle_NameFilter_ReturnsOnlyMatchingPlayLists()
         {

backend/Tests/Musify.Application.Tests/PlayLists/UpdatePlayListCommandHandlerTests.cs

@@ -62,6 +62,36 @@ namespace Musify.Application.Tests.PlayLists
             Assert.Equal(ErrorType.Unauthorized, result.FirstError.Type);
         }
 
+        [Fact]
+        public async Task Handle_NewVisibility_UpdatesIt()
+        {
+            var owner = TestEntities.User();
+            var playList = TestEntities.PlayList(owner.Id);
+            await SeedAsync(owner, playList);
+
+            var command = new UpdatePlayListCommand(owner.Id, playList.Id, null, null, null, Musify.Domain.ValueObjects.PlaylistVisibility.Public);
+
+            var result = await CreateHandler().Handle(command, TestContext.Current.CancellationToken);
+
+            Assert.False(result.IsError);
+            Assert.Equal(Musify.Domain.ValueObjects.PlaylistVisibility.Public, result.Value.Visibility);
+        }
+
+        [Fact]
+        public async Task Handle_NoVisibilitySpecified_LeavesItUnchanged()
+        {
+            var owner = TestEntities.User();
+            var playList = TestEntities.PlayList(owner.Id, visibility: Musify.Domain.ValueObjects.PlaylistVisibility.Public);
+            await SeedAsync(owner, playList);
+
+            var command = new UpdatePlayListCommand(owner.Id, playList.Id, "New Name", null, null);
+
+            var result = await CreateHandler().Handle(command, TestContext.Current.CancellationToken);
+
+            Assert.False(result.IsError);
+            Assert.Equal(Musify.Domain.ValueObjects.PlaylistVisibility.Public, result.Value.Visibility);
+        }
+
         [Fact]
         public async Task Handle_BlankNameAndDescription_LeavesThemUnchanged()
         {