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/player.html

@@ -219,9 +219,9 @@ body {
 <div class="player-card" id="player-card">
     <div class="player-artwork" id="artwork">
         <i class="mdi mdi-music-note" id="artwork-icon"></i>
-        <span class="live-badge" id="live-badge">LIVE</span>
+        <span class="live-badge" id="live-badge">{'LIVE'|t}</span>
     </div>
-    <div class="player-title" id="title">Loading...</div>
+    <div class="player-title" id="title">{'Loading...'|t}</div>
     <div class="player-progress-wrap" id="progress-wrap">
         <input type="range" class="player-progress" id="progress" min="0" max="100" value="0" step="0.1">
         <div class="player-time">
@@ -230,13 +230,13 @@ body {
         </div>
     </div>
     <div class="player-controls">
-        <button class="ctrl-btn sm" id="vol-btn" title="Mute/Unmute">
+        <button class="ctrl-btn sm" id="vol-btn" title="{'Mute/Unmute'|t}">
             <i class="mdi mdi-volume-high" id="vol-icon"></i>
         </button>
-        <button class="ctrl-btn lg" id="play-btn" title="Play/Pause">
+        <button class="ctrl-btn lg" id="play-btn" title="{'Play/Pause'|t}">
             <i class="mdi mdi-play" id="play-icon"></i>
         </button>
-        <button class="ctrl-btn sm close" id="close-btn" title="Stop & Close">
+        <button class="ctrl-btn sm close" id="close-btn" title="{'Stop & Close'|t}">
             <i class="mdi mdi-close"></i>
         </button>
     </div>