[fix] scaling of result page on small screens by @ZetaTom

* thanks to https://github.com/ZetaTom for the fix!
* set the width of the input#q element to 100% of the 1fr space of the grid layout
* change the viewport meta tag to th recommended value (see: https://developer.mozilla.org/en-US/docs/Web/HTML/Viewport_meta_tag#viewport_basics)
* add a new @ultra-small-phone width of 20rem; when a device is smaller than that the search logo does not get displayed on the result page anymore