Refactor: Email statt Username als Anzeige-Identifier

- Header zeigt volle Email statt Username
- Lagen-Karten/Sidebar zeigen Email-Prefix (vor dem @) als Ersteller
- Feedback-Emails nutzen Email-Prefix statt Username
- Login/Notification-Emails nutzen Email-Prefix als Anrede
- DB-Queries holen email statt username für Ersteller-Anzeige

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

src/static/js/components.js

@@ -22,7 +22,7 @@ const UI = {
         const isRefreshing = App._refreshingIncidents && App._refreshingIncidents.has(incident.id);
         const dotClass = isRefreshing ? 'refreshing' : (incident.status === 'active' ? 'active' : 'archived');
         const activeClass = isActive ? 'active' : '';
-        const creator = incident.created_by_username || '';
+        const creator = (incident.created_by_username || '').split('@')[0];
 
         return `
             <div class="incident-item ${activeClass}" data-id="${incident.id}" onclick="App.selectIncident(${incident.id})" role="button" tabindex="0">