docs: update docs icons (#12465)

### What problem does this PR solve?

Update icons for docs.
Trailing spaces are auto truncated by the editor, does not affect real
content.

### Type of change

- [x] Documentation Update

docs/guides/agent/agent_introduction.md

@@ -1,6 +1,9 @@
 ---
 sidebar_position: 1
 slug: /agent_introduction
+sidebar_custom_props: {
+  categoryIcon: LucideBookOpenText
+}
 ---
 
 # Introduction to agents
@@ -24,7 +27,7 @@ Agents and RAG are complementary techniques, each enhancing the other’s capabi
 
 :::tip NOTE
 
-Before proceeding, ensure that:  
+Before proceeding, ensure that:
 
 1. You have properly set the LLM to use. See the guides on [Configure your API key](../models/llm_api_key_setup.md) or [Deploy a local LLM](../models/deploy_local_llm.mdx) for more information.
 2. You have a dataset configured and the corresponding files properly parsed. See the guide on [Configure a dataset](../dataset/configure_knowledge_base.md) for more information.
@@ -41,7 +44,7 @@ We also provide templates catered to different business scenarios. You can eithe
 
    ![agent_template](https://raw.githubusercontent.com/infiniflow/ragflow-docs/main/images/agent_template_list.jpg)
 
-2. To create an agent from scratch, click **Create Agent**. Alternatively, to create an agent from one of our templates, click the desired card, such as **Deep Research**, name your agent in the pop-up dialogue, and click **OK** to confirm.  
+2. To create an agent from scratch, click **Create Agent**. Alternatively, to create an agent from one of our templates, click the desired card, such as **Deep Research**, name your agent in the pop-up dialogue, and click **OK** to confirm.
 
    *You are now taken to the **no-code workflow editor** page.*