Add client usage guide for UltimateAuth

Added a comprehensive client usage guide for UltimateAuth, detailing its features, architecture, core concepts, examples, and state events.

Author: mckaragoz

docs/content/client/index.md

@@ -0,0 +1,96 @@
+# 🚀 Client Usage Guide
+
+UltimateAuth Client is a **high-level SDK** designed to simplify authentication flows.
+
+It is NOT just an HTTP wrapper.
+
+## 🧠 What Makes the Client Different?
+
+The client:
+
+- Handles full authentication flows (login, PKCE, refresh)
+- Manages redirects automatically
+- Publishes state events
+- Provides structured results
+- Works across multiple client types (SPA, server, hybrid)
+
+👉 You SHOULD use the client instead of calling endpoints manually.
+
+<br>
+
+## 🧱 Client Architecture
+
+The client is split into multiple specialized services:
+
+| Service              | Responsibility                      |
+|----------------------|-------------------------------------|
+| FlowClient           | Login, logout, refresh, PKCE        |
+| SessionClient        | Session & device management         |
+| UserClient           | User profile & lifecycle            |
+| IdentifierClient     | Email / username / phone management |
+| CredentialClient     | Password management                 |
+| AuthorizationClient  | Roles & permissions                 |
+
+<br>
+
+## 🔑 Core Concept: Flow-Based Design
+
+UltimateAuth is **flow-oriented**, not endpoint-oriented.
+
+Instead of calling endpoints:
+
+❌ POST /auth/login  
+✔ flowClient.LoginAsync()
+
+<br>
+
+## ⚡ Example
+
+```csharp
+await flowClient.LoginAsync(new LoginRequest
+{
+    Identifier = "user@ultimateauth.com",
+    Secret = "password"
+});
+```
+
+👉 This automatically:
+
+- Builds request payload
+- Handles redirect
+- Integrates with configured endpoints
+
+<br>
+
+## 🔄 State Events
+
+Client automatically publishes events:
+
+- SessionRevoked
+- ProfileChanged
+- AuthorizationChanged
+
+<br>
+
+## 🧭 How to Use This Section
+
+Follow these guides:
+
+- authentication.md → login, refresh, logout
+- session-management.md → sessions & devices
+- user-management.md → user operations
+- identifiers.md → login identifiers
+- authorization.md → roles & permissions
+
+## 🎯 Summary
+
+UltimateAuth Client:
+
+- abstracts complexity
+- enforces correct flows
+- reduces security mistakes
+
+
+👉 Think of it as:
+
+**“Authentication runtime for your frontend / app”**