Add asset pipeline and professionalize theme

Introduce a Node build system for minified CSS/JS with content hashes,
add PWA support, i18n helpers, accessibility improvements, and more
translatable strings. Move theme configuration from bookmarks to
localStorage, add Playwright tests, and set up CI workflows.

shaarli-pro/opensearch.html

@@ -1,12 +1,12 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <OpenSearchDescription xmlns="http://a9.com/-/spec/opensearch/1.1/">
-    <ShortName>Shaarli search - {$pagetitle}</ShortName>
-    <Description>Shaarli search - {$pagetitle}</Description>
+    <ShortName>{'Shaarli search'|t} - {$pagetitle}</ShortName>
+    <Description>{'Shaarli search'|t} - {$pagetitle}</Description>
     <Url type="text/html" template="{$serverurl}?searchterm={searchTerms}" />
     <Url type="application/atom+xml" template="{$serverurl}feed/atom?searchterm={searchTerms}"/>
     <Url type="application/rss+xml" template="{$serverurl}feed/rss?searchterm={searchTerms}"/>
     <InputEncoding>UTF-8</InputEncoding>
-    <Developer>Shaarli Community - https://github.com/shaarli/Shaarli/</Developer>
+    <Developer>{'Shaarli Community'|t} - https://github.com/shaarli/Shaarli/</Developer>
     <Image width="16" height="16">data:image/x-icon;base64,iVBORw0KGgoAAAANSUhEUgAAABgAAAAYCAYAAADgdz34AAAABmJLR0QA/wD/AP+gvaeTAAAHRklE
         QVRIx5WWaWxU5xWG3++7986dfYYZb+MN2xiMDRiDFePUiQsNoiwpUNpAmhInJVEqpa0oQUlbJVKq
         olaiqpLKUtOKhAJRm1BKRVWctuykpFjAgPcFx/uMl5mxPTOeuXPv3O3rjyiV0lIpfX+dc36c55xf