README update: small copy updates, new intro video, and short blurb on Appsmith Agents (#40359)

## Description
> [!TIP]  
> _Add a TL;DR when the description is longer than 500 words or
extremely technical (helps the content, marketing, and DevRel team)._
>
> _Please also include relevant motivation and context. List any
dependencies that are required for this change. Add links to Notion,
Figma or any other documents that might be relevant to the PR._


Fixes #`Issue Number`  
_or_  
Fixes `Issue URL`
> [!WARNING]  
> _If no issue exists, please create an issue first, and check with the
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## Automation

/ok-to-test tags=""

### 🔍 Cypress test results
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> If you modify the content in this section, you are likely to disrupt
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## Communication
Should the DevRel and Marketing teams inform users about this change?
- [ ] Yes
- [x] No


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Documentation**
- Updated the README to broaden the description of application types and
highlight enhanced platform capabilities.
  - Revised the introductory video and its thumbnail.
- Added a new section introducing "Appsmith Agents," detailing AI
integration features and providing a link for more information.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

README.md

@@ -25,9 +25,9 @@
 
 ---
 
-Organizations build internal applications such as dashboards, database GUIs, admin panels, approval apps, customer support dashboards, and more to help their teams perform day-to-day operations. Appsmith is an open-source tool that enables the rapid development of these internal apps. Read more on our [website](https://www.appsmith.com?utm_source=github&utm_medium=organic&utm_campaign=readme).
+Organizations build custom applications like dashboards, admin panels, customer 360, IT automation, and service management tools to help their teams work more efficiently and effectively. Appsmith is an open-source low-code platform that streamlines custom application development, deployment, and maintenance. Learn more on our [website](https://www.appsmith.com?utm_source=github&utm_medium=organic&utm_campaign=readme).
   
-[![Appsmith in 100 secs](/static/images/appsmith-in-100-seconds.png)](https://www.youtube.com/watch?v=NnaJdA1A11s?v=Dxe_NzdGzL4&utm_source=github&utm_medium=organic&utm_campaign=readme/?target=_blank)  
+[![Appsmith in 100 secs](/static/images/appsmith-introduction-video-tile.png)](https://www.youtube.com/watch?v=jhyDI0e1o08?v=Dxe_NzdGzL4&utm_source=github&utm_medium=organic&utm_campaign=readme/?target=_blank)  
 
 
 ## Installation
@@ -59,6 +59,8 @@ To build and run Appsmith in your local dev environment, see [Setup for local de
 - [Community Portal](https://community.appsmith.com/?utm_source=github&utm_medium=organic&utm_campaign=readme)
 - [support@appsmith.com](mailto:support@appsmith.com)
 
+## Appsmith Agents
+Introducing a new agentic AI platform that integrates the latest AI models with private and proprietary data at scale — inside the tools and systems that teams use every day. Appsmith Agents expands generative AI’s capabilities for the millions of knowledge workers in sales, support, customer success, human resources, and other business teams. By giving continuous context to AI models, Appsmith Agents lets teams ask questions and configure automations specific to their business without model fine-tuning or complex RAG implementations. Visit [appsmith.com/ai](https://www.appsmith.com/ai) to learn more.
                                                                                                                 
 ## Contributing
 We ❤️ our contributors. We're committed to fostering an open, welcoming, and safe environment in the community.