docs: add user access controls and content discovery to AI agents

guides/ai-agents.mdx

@@ -42,6 +42,7 @@ Getting started with AI agents is simple - you can begin using them right away o
    - **Name and image** - Give your agent a memorable name and visual identity
    - **Instructions (optional)** - Provide context about your models, tables, or specific use cases to help the AI give more relevant responses
    - **Tags (optional)** - Use tags to control which metrics and dimensions the agent can access
+   - **User and Group Access** - Control which users and groups can access your agent through the agent settings
 
 Once set up, you can start asking questions immediately! Try asking "What kind of data can you access?" to get started.
 
@@ -61,6 +62,7 @@ AI agents in Lightdash allow you to:
 - **Maintain conversation context** - AI agents remember your conversation history, so you can build on previous questions and refine your analysis
 - **Provide text-only responses** - Get answers in natural language when visualizations aren't needed
 - **Guide you to the right data** - Direct you to the most relevant explores or tables for your questions
+- **Discover existing content** - Find and share relevant charts and dashboards that have already been created in your project
 
 ### Using AI agents in Slack