Add Ping backend

.NET 10 solution for Ping, a Discord style chat app: Domain, Application
and Infrastructure projects plus the Api host. SignalR for chat and
presence, LiveKit for call tokens, EF Core on Postgres, S3 compatible
storage for attachments, and OIDC auth shared with the Musify Zitadel
instance. Includes the Compose stack for local development.

backend/Core/Ping.Domain/Entities/Attachment.cs

@@ -0,0 +1,41 @@
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+using Ping.Domain.ValueObjects;
+
+namespace Ping.Domain.Entities
+{
+    [Table("Attachment")]
+    public class Attachment
+    {
+        [Key]
+        public Guid Id { get; set; }
+
+        public required Guid MessageId { get; set; }
+
+        public Message? Message { get; set; }
+
+        [Required]
+        [MaxLength(255)]
+        public required string Bucket { get; set; }
+
+        [Required]
+        [MaxLength(1024)]
+        public required string Key { get; set; }
+
+        [Required]
+        [MaxLength(255)]
+        public required string FileName { get; set; }
+
+        [Required]
+        [MaxLength(255)]
+        public required string ContentType { get; set; }
+
+        public required long SizeBytes { get; set; }
+
+        [Required]
+        public AttachmentKind Kind { get; set; }
+
+        [Required]
+        public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+    }
+}

backend/Core/Ping.Domain/Entities/Channel.cs

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+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+using Ping.Domain.ValueObjects;
+
+namespace Ping.Domain.Entities
+{
+    [Table("Channel")]
+    public class Channel
+    {
+        [Key]
+        public Guid Id { get; set; }
+
+        public Guid? ServerId { get; set; }
+
+        public Server? ServerNavigation { get; set; }
+
+        [MaxLength(100)]
+        public string? Name { get; set; }
+
+        [MaxLength(1024)]
+        public string? Topic { get; set; }
+
+        [Required]
+        public ChannelType Type { get; set; }
+
+        [Required]
+        public int Position { get; set; }
+
+        [Required]
+        public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+        public ICollection<ChannelMember> Members { get; set; } = new List<ChannelMember>();
+    }
+}

backend/Core/Ping.Domain/Entities/ChannelMember.cs

@@ -0,0 +1,13 @@
+namespace Ping.Domain.Entities
+{
+    public class ChannelMember
+    {
+        public required Guid ChannelId { get; set; }
+
+        public Channel? Channel { get; set; }
+
+        public required long UserId { get; set; }
+
+        public User? User { get; set; }
+    }
+}

backend/Core/Ping.Domain/Entities/Friendship.cs

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+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+using Ping.Domain.ValueObjects;
+
+namespace Ping.Domain.Entities
+{
+    [Table("Friendship")]
+    public class Friendship
+    {
+        [Key]
+        public Guid Id { get; set; }
+
+        public required long RequesterId { get; set; }
+
+        public User? Requester { get; set; }
+
+        public required long AddresseeId { get; set; }
+
+        public User? Addressee { get; set; }
+
+        [Required]
+        public FriendshipStatus Status { get; set; } = FriendshipStatus.Pending;
+
+        public long? BlockedById { get; set; }
+
+        [Required]
+        public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+        public DateTime? RespondedAt { get; set; }
+    }
+}

backend/Core/Ping.Domain/Entities/Message.cs

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+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Ping.Domain.Entities
+{
+    [Table("Message")]
+    public class Message
+    {
+        [Key]
+        public Guid Id { get; set; }
+
+        public required Guid ChannelId { get; set; }
+
+        public Channel? Channel { get; set; }
+
+        public required long AuthorId { get; set; }
+
+        public User? Author { get; set; }
+
+        [Required]
+        [MaxLength(4000)]
+        public required string Content { get; set; }
+
+        public Guid? ReplyToMessageId { get; set; }
+
+        [Required]
+        public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+        public DateTime? EditedAt { get; set; }
+
+        public DateTime? DeletedAt { get; set; }
+
+        public ICollection<Attachment> Attachments { get; set; } = new List<Attachment>();
+    }
+}

backend/Core/Ping.Domain/Entities/Server.cs

@@ -0,0 +1,34 @@
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+using Ping.Domain.Abstractions;
+
+namespace Ping.Domain.Entities
+{
+    [Table("Server")]
+    public class Server : IAuditable
+    {
+        [Key]
+        public Guid Id { get; set; }
+
+        [Required]
+        [MaxLength(100)]
+        public required string Name { get; set; }
+
+        [MaxLength(2048)]
+        public string? IconUrl { get; set; }
+
+        public required long OwnerId { get; set; }
+
+        public User? Owner { get; set; }
+
+        [Required]
+        public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+        [Required]
+        public DateTime UpdatedAt { get; set; } = DateTime.UtcNow;
+
+        public ICollection<ServerMember> Members { get; set; } = new List<ServerMember>();
+
+        public ICollection<Channel> Channels { get; set; } = new List<Channel>();
+    }
+}

backend/Core/Ping.Domain/Entities/ServerMember.cs

@@ -0,0 +1,27 @@
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+using Ping.Domain.ValueObjects;
+
+namespace Ping.Domain.Entities
+{
+    [Table("ServerMember")]
+    public class ServerMember
+    {
+        public required Guid ServerId { get; set; }
+
+        public Server? Server { get; set; }
+
+        public required long UserId { get; set; }
+
+        public User? User { get; set; }
+
+        [MaxLength(64)]
+        public string? Nickname { get; set; }
+
+        [Required]
+        public ServerMemberRole Role { get; set; } = ServerMemberRole.Member;
+
+        [Required]
+        public DateTime JoinedAt { get; set; } = DateTime.UtcNow;
+    }
+}

backend/Core/Ping.Domain/Entities/User.cs

@@ -0,0 +1,36 @@
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+using Ping.Domain.Abstractions;
+
+namespace Ping.Domain.Entities
+{
+    [Table("User")]
+    public class User : IAuditable
+    {
+        [Key]
+        [DatabaseGenerated(DatabaseGeneratedOption.None)]
+        public required long Id { get; set; }
+
+        [Required]
+        [MaxLength(64)]
+        public required string Username { get; set; }
+
+        [Required]
+        [MaxLength(64)]
+        public required string NormalizedUsername { get; set; }
+
+        [MaxLength(64)]
+        public string? DisplayName { get; set; }
+
+        [MaxLength(2048)]
+        public string? AvatarUrl { get; set; }
+
+        [Required]
+        public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+        [Required]
+        public DateTime UpdatedAt { get; set; } = DateTime.UtcNow;
+
+        public ICollection<ServerMember> ServerMemberships { get; set; } = new List<ServerMember>();
+    }
+}