feat: Add IRC gateway functionality and update documentation

docs/articles/architecture.md

@@ -4,6 +4,16 @@
 
 EchoHub follows a decentralized model where each server is fully independent. There is no central authority or account federation. Users create one account per server.
 
+The server exposes two protocol interfaces to the same chat backend:
+
+```text
+IRC Client ──► TCP :6667 ──► IrcGateway ──┐
+                                           ├──► ChatService ──► DB + PresenceTracker
+TUI Client ──► WebSocket ──► ChatHub ─────┘
+```
+
+Both protocols call into a shared `IChatService` for business logic. Events fan out to all registered `IChatBroadcaster` implementations (SignalR and IRC).
+
 ## Components
 
 ### EchoHub.Core
@@ -12,7 +22,7 @@ Shared library containing:
 
 - **Models**: `User`, `Channel`, `Message`, `RefreshToken`
 - **DTOs**: Record types for API requests/responses
-- **Contracts**: `IEchoHubClient` -- the strongly-typed SignalR client interface
+- **Contracts**: `IChatService` (protocol-agnostic chat operations), `IChatBroadcaster` (event fan-out interface), `IEchoHubClient` (SignalR client interface)
 - **Constants**: `ValidationConstants` (shared regex patterns), `HubConstants`
 
 ### EchoHub.Server
@@ -20,10 +30,21 @@ Shared library containing:
 ASP.NET Core web application:
 
 - **Controllers**: REST API endpoints for auth, channels, users, files, server info
-- **Hubs**: SignalR `ChatHub` for real-time messaging
+- **Hubs**: SignalR `ChatHub` -- thin adapter delegating to `IChatService`
 - **Auth**: JWT token service (15-min access tokens, 30-day refresh tokens)
 - **Data**: EF Core with SQLite
-- **Services**: Presence tracking, file storage, image-to-ASCII conversion
+- **Services**: `ChatService` (core business logic), `SignalRBroadcaster`, presence tracking, file storage, image-to-ASCII conversion
+
+### EchoHub.Server.Irc
+
+IRC protocol gateway (separate project for clean separation of concerns):
+
+- **IrcGatewayService**: `BackgroundService` with TCP listener on configured port(s), optional TLS
+- **IrcCommandHandler**: Per-client IRC command dispatch -- handles `CAP`/`SASL`, `NICK`/`USER`/`PASS`, `JOIN`/`PART`/`PRIVMSG`/`QUIT`, `NAMES`/`TOPIC`/`WHO`/`WHOIS`/`AWAY`/`LIST`/`MODE`/`MOTD`
+- **IrcBroadcaster**: `IChatBroadcaster` implementation that formats chat events as IRC protocol lines, with echo suppression (IRC convention)
+- **IrcMessageFormatter**: Converts `MessageDto` to IRC `PRIVMSG` lines -- splits long text at word boundaries (~400 byte chunks), sends images as ASCII art line-by-line
+
+IRC users authenticate with existing EchoHub accounts via `PASS`/`NICK`/`USER` or SASL PLAIN (BCrypt verification against the database).
 
 ### EchoHub.Client
 
@@ -31,11 +52,22 @@ Terminal.Gui v2 TUI application:
 
 - **UI**: Main window, dialogs, chat renderer with ANSI color support
 - **Services**: API client with automatic token refresh, SignalR connection wrapper
-- **Themes**: 6 built-in color themes
+- **Themes**: 13 built-in color themes
 - **Config**: Client configuration management
 
 ## Communication
 
-- REST API for authentication, profile management, channel CRUD, file uploads
-- SignalR WebSocket for real-time messaging and presence updates
+- **REST API** for authentication, profile management, channel CRUD, file uploads
+- **SignalR WebSocket** for real-time messaging and presence updates (TUI client)
+- **IRC TCP** for real-time messaging via standard IRC protocol (IRC clients)
 - JWT tokens passed via query string for SignalR authentication
+- IRC authentication via PASS/SASL PLAIN against BCrypt password hashes
+
+## Broadcaster Pattern
+
+The `IChatBroadcaster` interface allows multiple protocols to receive chat events:
+
+- **SignalRBroadcaster**: Wraps `IHubContext<ChatHub>`, filters out IRC connections
+- **IrcBroadcaster**: Iterates live IRC connections in a channel, formats events as IRC protocol lines
+
+Both are registered in DI and called by `ChatService` when events occur. This means a message sent from an IRC client appears in the TUI client, and vice versa.