feat: Update ppt-review task (#141)

[Oleksandr123234]

This change brings the following improvements to the "ppt-review" task:

1. Updated guidelines to clearly define the required steps for installing the tool for reviewing PowerPoint (PPT) presentations.
2. Updated agent description to manage user expectations by clearly stating the capabilities of the agent. Users currently expect it to perform advanced tasks such as designing slides, attaching media, etc., which are beyond its scope.

Besides, this change also add a new task called "create-diagram". It is useful for creating mermaid diagrams for the documentation pages.

[Oleksandr123234]

/rechek