fix(release): fehlende Versionsnummern + bgUrl-Validierung

Drei Stellen hatten noch '2.0.0' statt '2.0.1': newtab.html About-Sektion,
data.js Export und app.js Backup-Export. FileReader-Upload in settings.js
validiert jetzt bgUrl via isValidBgUrl() (Defense-in-Depth).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

newtab.html

@@ -223,7 +223,7 @@
     <div class="panel-footer">
       <div class="about-block">
         <div class="about-logo" data-i18n="about.title">⬡ HELLION NEWTAB</div>
-        <div class="about-version">Version 2.0.0 · by Hellion Online Media</div>
+        <div class="about-version">Version 2.0.1 · by Hellion Online Media</div>
 
         <div class="about-links">
           <a href="https://hellion-media.de/impressum" target="_blank" class="about-link">