[Bug] (docs): User Experience - Life of Task - Content Flow issue (Stateless vs Stateful Task)

### What happened?

* Page URL: https://a2a-protocol.org/latest/topics/life-of-a-task/
* Problem: The "Life of a Task" page has a confusing flow and does not clearly explain the decision-making process for choosing between a stateless message and a stateful task.
* Proposed Fix: Restructure the documentation to have a more intuitive flow, add an "Overview" section, use explicit terminology, and create a flowchart to illustrate the distinction between Messages and Tasks.
* Justification: This will make the documentation easier to follow and understand.

### 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 'Life of a Task' documentation page at https://a2a-protocol.org/latest/topics/life-of-a-task/. Start by reading the current page to understand its structure and the confusing flow. Then, propose a restructured outline with an 'Overview' section, clearer terminology, and a flowchart to distinguish Messages and Tasks. Check the repository's documentation source files (likely in a 'docs' directory) to see how the page is built and where to make edits.

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