Use normalize_whitespace for head meta description

Fixes #800 (closed)

This MR utilizes normalize_whitespace (available since Jekyll 3.2) in the pages' html meta description tags.

Internally, the filter performs a

.gsub(/\s+/, " ").strip

which conveniently coalesces contiguous whitespaces (including line breaks) into a single space.

Eg: TWIF 9 Oct 2025

Current F-Droid website:

                                                       ❗                                            ❗            ❗
  <meta name="description" content="This Week in F-DroidTWIF curated on Thursday, 09 Oct 2025, Week 41Community NewsThe end of tt-rss.org might be a reason to be sad. We have at least two apps ...">

  <meta property="og:description" content="This Week in F-DroidTWIF curated on Thursday, 09 Oct 2025, Week 41Community NewsThe end of tt-rss.org might be a reason to be sad. We have at least two apps ...">
                                                              ❗                                            ❗            ❗

This MR:

                                                        ✅                                             ✅             ✅
  <meta name="description" content="This Week in F-Droid TWIF curated on Thursday, 09 Oct 2025, Week 41 Community News The end of tt-rss.org might be a reason to be sad. We have at least two ap...">

  <meta property="og:description" content="This Week in F-Droid TWIF curated on Thursday, 09 Oct 2025, Week 41 Community News The end of tt-rss.org might be a reason to be sad. We have at least two ap...">
                                                               ✅                                             ✅             ✅