use css truncate everywhere and remove StringUtils.truncate function (#513)

Co-authored-by: robs <git@robs.social>

lib/pinchflat_web/controllers/sources/source_html/show.html.heex

@@ -1,9 +1,9 @@
 <div class="mb-6 flex gap-3 flex-row items-center justify-between">
-  <div class="flex gap-3 items-center">
+  <div class="flex gap-3 items-center min-w-0">
     <.link href={~p"/sources"}>
       <.icon name="hero-arrow-left" class="w-10 h-10 hover:dark:text-white" />
     </.link>
-    <h2 class="text-title-md2 font-bold text-black dark:text-white ml-4">
+    <h2 class="text-title-md2 font-bold text-black dark:text-white ml-4 truncate">
       {@source.custom_name}
     </h2>
   </div>