For the "Kiwix App" section, consider having a "Progressive Web App" category in dropdown

@Popolechien This is a suggested solution for the dilemma raised in #217. I suggest having a new entry in the dropdown on the download page. This could be "Progressive Web App" (or "PWA" if latter is too long).

This would allow having a dedicated tile for the PWA, explaining what it is compatible with and where it can be installed. If you like the idea, I can provide some suggested text.

NB This would not supersede the UWP and Electron version listed on the Windows tile, as those are installable packages from app stores or GitHub releases, very different backend to the PWA.

Start at the download page's dropdown and the "Kiwix App" section, then trace how dropdown entries map to tiles. The work is done when a Progressive Web App or PWA category appears with a dedicated tile explaining compatibility and installation, without replacing the existing UWP or Electron entries.

Written by the indexing model from the issue text.