[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

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