[Bug](docs): User Experience - A2A docs HomePage needs a revamp/re-ordering

### What happened?

A2A HomePage would need a revamp to address following problems
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* **Problem 01:** Information about supported SDKs (Python, JavaScript, Java, C#, GoLang) is buried deep in the page and not immediately visible to developers.
* **Proposed Fix:** Move the SDK information to the top of the page. (As found in https://google.github.io/adk-docs/)
* **Justification:** This will provide a clear entry point for new users, making it easier for them to learn about A2A and its capabilities.

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* **Problem02:** A visual aid is located in the “Why use A2A protocol” section but would be more effective in the “What is A2A protocol” section.
* **Proposed Fix:** Move the image to the “What is A2A protocol” section.
* **Justification:** This will create a more intuitive and streamlined user interface by placing the visual aid in a more logical context.

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* **Problem03:** (When seen from a laptops/tablets) The homepage gives the first immediate impression that users can watch a YouTube video or DLAI take a course to get started, rather than being able to learn directly from the documentation. (Youtube Video & DLAI course appears before other key link to GetStart)
* **Proposed Fix:** Add a Table of Contents or re-arrange the content flow to introduce concepts first and then redirect them to the other sites.
* **Justification:** This will provide a clear and structured path for users to get started with A2A directly from the documentation.

### Relevant log output

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### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

The issue is about the A2A documentation homepage. Find the homepage source file (likely in a docs/ directory, possibly an index.md or README.md). Review the current layout to locate the SDK information, the visual aid image, and the placement of the YouTube/DLAI course links. Reorder sections as described: move SDK info to the top, relocate the image to the 'What is A2A protocol' section, and adjust content flow to prioritize documentation links. Verify changes by building or previewing the docs locally.

Scritto dal modello di indicizzazione a partire dal testo della issue.