Convert 4 pages to HTML admonitions

[rollsicecream]

Changes proposed in this PR:

• Convert

  • "Frontends" page
  • "Notebooks" page
  • "Password managers" page
  • "Productivity tools" page

To HTML admonitions.

And so, the HTML admonitions saga for the recommendations category has ended 🎉

But we now have to convert all Knowledge Base pages to HTML admonitions 😄

• I have disclosed any relevant conflicts of interest in my post.
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• I am the sole author of this work.
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