docs: update API documentation and changelog for v0.2.5 release

docs/api/client-articles/index.md

@@ -5,7 +5,9 @@ Articles related to the EchoHub TUI client built with Terminal.Gui v2.
 ## Topics
 
 - Terminal.Gui v2 patterns and conventions
-- Theme system and customization
+- Theme system and customization (including transparent theme)
 - Command system reference
-- Configuration management
+- Configuration and session persistence
+- Audio playback and file downloads
+- Automatic update checking
 - [Notification sounds](../../articles/notification-sounds.md)

docs/api/core-articles/index.md

@@ -5,5 +5,5 @@ Articles related to the EchoHub.Core shared library.
 ## Topics
 
 - Data models and DTOs
-- Contract interfaces (IChatService, IChatBroadcaster, IEchoHubClient)
+- Contract interfaces (IChatService, IChannelService, IChatBroadcaster, IEchoHubClient)
 - Validation constants and shared rules

docs/api/index.md

@@ -10,11 +10,11 @@ Terminal.Gui v2 TUI application -- UI components, services, themes, and configur
 
 ### Core
 
-Shared library -- DTOs, models, constants, and contracts (`IChatService`, `IChatBroadcaster`, `IEchoHubClient`).
+Shared library -- DTOs, models, constants, and contracts (`IChatService`, `IChannelService`, `IChatBroadcaster`, `IEchoHubClient`).
 
 ### Server
 
-ASP.NET Core server -- controllers, hubs, ChatService, SignalRBroadcaster, authentication, and data access.
+ASP.NET Core server -- controllers, hubs, ChatService, ChannelService, SignalRBroadcaster, authentication, file cleanup, and data access.
 
 ### Server.Irc
 

docs/api/server-articles/index.md

@@ -8,6 +8,7 @@ Articles related to the EchoHub server built with ASP.NET Core.
 - SignalR hub and real-time messaging
 - IRC gateway and protocol bridging
 - ChatService and broadcaster pattern
-- File upload and validation
+- ChannelService and channel CRUD
+- File upload, validation, and cleanup
 - Rate limiting configuration
-- Database schema and migrations
+- Database schema, migrations, and DataMigrationService