fix: Tote src-type-display Referenzen entfernt (Element existiert nicht im HTML)

discoverSource() und editSource() referenzierten ein nicht existierendes
DOM-Element src-type-display, was beim Hinzufügen/Bearbeiten von Quellen
den Fehler "Cannot set properties of null (setting value)" auslöste.
src-type-select wird bereits korrekt mit Null-Check gesetzt.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/static/js/app.js

@@ -2731,7 +2731,6 @@ const App = {
                 const typeLabel = this._discoveredData.source_type === 'rss_feed' ? 'RSS-Feed' : this._discoveredData.source_type === 'telegram_channel' ? 'Telegram' : 'Web-Quelle';
                 const typeSelect = document.getElementById('src-type-select');
                 if (typeSelect) typeSelect.value = this._discoveredData.source_type || 'web_source';
-                document.getElementById('src-type-display').value = typeLabel;
 
                 const rssGroup = document.getElementById('src-rss-url-group');
                 const rssInput = document.getElementById('src-rss-url');
@@ -2811,7 +2810,6 @@ const App = {
         const typeLabel = source.source_type === 'rss_feed' ? 'RSS-Feed' : source.source_type === 'telegram_channel' ? 'Telegram' : 'Web-Quelle';
         const typeSelect = document.getElementById('src-type-select');
         if (typeSelect) typeSelect.value = source.source_type || 'web_source';
-        document.getElementById('src-type-display').value = typeLabel;
 
         const rssGroup = document.getElementById('src-rss-url-group');
         const rssInput = document.getElementById('src-rss-url');