[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

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