Add fundamentals section to documentation

Author: mckaragoz

docs/content/fundamentals/index.md

@@ -0,0 +1,12 @@
+# 🧠 Fundamentals
+
+This section explains how UltimateAuth works internally.
+
+If you are new, follow this order:
+
+1. [Authentication Model](./auth-model.md)
+2. [Flow-Based Authentication](./flow-based-auth.md)
+3. [Authentication Modes](./auth-modes.md)
+4. [Client Profiles](./client-profiles.md)
+5. [Runtime Architecture](./runtime-architecture.md)
+6. [Request Lifecycle](./request-lifecycle.md)