docs: add new Agent landing page (#800)

Updates the NGINX Agent v2 docs landing page to the new format with featured docs and cards

Author: JTorreG

content/agent/_index.md

@@ -9,4 +9,50 @@ cascade:
     start-date: 2025-05-29
     end-date: 2025-09-09
     md: /_banners/agent-v3-release.md
+# The subtitle displays directly underneath the heading of a given page
+nd-subtitle:
+# Indicates that this is a custom landing page
+nd-landing-page: true
+# Types have a 1:1 relationship with Hugo archetypes, so you shouldn't need to change this
+nd-content-type: landing-page
+# Intended for internal catalogue and search, case sensitive:
+# Agent, N4Azure, NIC, NIM, NGF, NAP-DOS, NAP-WAF, NGINX One, NGINX+, Solutions, Unit
+nd-product: Agent
 ---
+
+## About
+
+NGINX Agent is a companion daemon for your NGINX Open Source or NGINX Plus instance. It enables remote management of NGINX
+configurations, collection and reporting of real-time NGINX performance and operating system metrics, and notifications of NGINX events.
+
+[//]: # "This initial section introduces the product to a reader: give a short 1-2 sentence summary of what the product does and its value to the reader."
+[//]: # "Name specific functionality it provides: avoid ambiguous descriptions such as 'enables efficiency', focus on what makes it unique."
+
+## Featured content
+[//]: # "You can add a maximum of three cards: any extra will not display."
+[//]: # "One card will take full width page: two will take half width each. Three will stack like an inverse pyramid."
+[//]: # "Some examples of content could be the latest release note, the most common install path, and a popular new feature."
+
+{{<card-layout>}}
+  {{<card-section showAsCards="true" isFeaturedSection="true">}}
+    {{<card title="About" titleUrl="/nginx-agent/about" icon="info">}}
+      Learn everything you need to know about NGINX Agent
+    {{</card>}}
+    <!-- The titleURL and icon are both optional -->
+    <!-- Lucide icon names can be found at https://lucide.dev/icons/ -->
+    {{<card title="Getting started" titleUrl="/nginx-agent/installation-upgrade/getting-started" icon="unplug">}}
+      Install NGINX Agent and run a mock control plane
+    {{</card>}}
+  {{</card-section>}}
+{{</card-layout>}}
+
+{{<card-layout>}}
+  {{<card-section showAsCards="true" isFeaturedSection="true">}}
+    {{<card title="Upgrade" titleUrl="/nginx-agent/installation-upgrade/upgrade/" icon="circle-fading-arrow-up">}}
+    {{</card>}}
+    {{<card title="Configuration" titleUrl="/nginx-agent/configuration" icon="cog">}}
+    {{</card>}}
+    {{<card title="Support" titleUrl="/nginx-agent/support" icon="hand-helping">}}
+    {{</card>}}
+  {{</card-section>}}
+{{</card-layout>}}