css: refactor CSS to use Tailwind-style utility classes.

Refactor CSS to use standard Tailwind-style utility classes instead of
ad-hoc rules. This eliminates a lot of single-purpose rules for specific
UI elements and standardizes margins to be more consistent throughout
the site.

Utility classes are defined manually on an as-needed basis instead of
importing Tailwind as a whole. Naming conventions mostly follow
Tailwind's conventions, otherwise they follow Bootstrap.

* https://tailwindcss.com/docs/
* https://getbootstrap.com/docs/5.0/utilities/spacing/

app/views/artists/index.html.erb

@@ -4,7 +4,7 @@
   <div id="a-index">
     <%= render "search" %>
 
-    <%= table_for @artists, class: "striped autofit" do |t| %>
+    <%= table_for @artists, class: "striped autofit", tr: { class: "h-10" } do |t| %>
       <% t.column "Name" do |artist| %>
         <%= link_to artist.name, artist, class: "tag-type-#{Tag.categories.artist}" %>
         <span class="post-count"><%= artist.tag.try(:post_count) || 0 %></span>