feat: add password protection for channels

- Updated IChatService to include password parameter in JoinChannelAsync method.
- Modified ChannelDto and related models to support password functionality.
- Implemented password handling in ChannelService for channel creation and membership validation.
- Enhanced IrcCommandHandler to manage channel join requests with passwords.
- Added ChannelPasswordDialog for user input when joining protected channels.
- Created database migration to add PasswordHash column to Channels table.
- Updated tests to cover new password functionality in channel joining and management.

src/EchoHub.Server/Data/EchoHubDbContext.cs

@@ -44,6 +44,7 @@ public class EchoHubDbContext : DbContext
             entity.HasIndex(c => c.Name).IsUnique();
             entity.Property(c => c.Name).IsRequired().HasMaxLength(100);
             entity.Property(c => c.Topic).HasMaxLength(500);
+            entity.Property(c => c.PasswordHash).HasMaxLength(100);
 
             entity.HasMany(c => c.Messages)
                   .WithOne(m => m.Channel)