feat: Add initial implementation of CI/CD workflows, documentation, and testing framework

docs/articles/architecture.md

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+# Architecture
+
+## Overview
+
+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.
+
+## Components
+
+### EchoHub.Core
+
+Shared library containing:
+
+- **Models**: `User`, `Channel`, `Message`, `RefreshToken`
+- **DTOs**: Record types for API requests/responses
+- **Contracts**: `IEchoHubClient` -- the strongly-typed SignalR client interface
+- **Constants**: `ValidationConstants` (shared regex patterns), `HubConstants`
+
+### EchoHub.Server
+
+ASP.NET Core web application:
+
+- **Controllers**: REST API endpoints for auth, channels, users, files, server info
+- **Hubs**: SignalR `ChatHub` for real-time messaging
+- **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
+
+### EchoHub.Client
+
+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
+- **Config**: Client configuration management
+
+## Communication
+
+- REST API for authentication, profile management, channel CRUD, file uploads
+- SignalR WebSocket for real-time messaging and presence updates
+- JWT tokens passed via query string for SignalR authentication

docs/articles/getting-started.md

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+# Getting Started
+
+## Prerequisites
+
+- [.NET 10 SDK](https://dotnet.microsoft.com/download)
+
+## Run the Server
+
+```bash
+dotnet run --project src/EchoHub.Server
+```
+
+On first run, the server automatically:
+
+1. Creates `appsettings.json` from the example config
+2. Generates a secure JWT secret
+3. Creates the SQLite database with a `#general` channel
+
+## Run the Client
+
+```bash
+dotnet run --project src/EchoHub.Client
+```
+
+Connect to a server, register an account, and start chatting.
+
+## Build from Source
+
+```bash
+dotnet build src/EchoHub.slnx
+```

docs/articles/toc.yml

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+- name: Getting Started
+  href: getting-started.md
+- name: Architecture
+  href: architecture.md