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/app.js

@@ -430,8 +430,8 @@ const App = {
 
         try {
             const user = await API.getMe();
-            this._currentUsername = user.username;
-            document.getElementById('header-user').textContent = user.username;
+            this._currentUsername = user.email;
+            document.getElementById('header-user').textContent = user.email;
 
             // Org-Name anzeigen
             const orgNameEl = document.getElementById('header-org-name');
@@ -668,14 +668,14 @@ const App = {
         // Ersteller anzeigen
         const creatorEl = document.getElementById('incident-creator');
         if (creatorEl) {
-            creatorEl.textContent = incident.created_by_username || '';
+            creatorEl.textContent = (incident.created_by_username || '').split('@')[0];
         }
 
         // Delete-Button: nur Ersteller darf löschen
         const deleteBtn = document.getElementById('delete-incident-btn');
         const isCreator = incident.created_by_username === this._currentUsername;
         deleteBtn.disabled = !isCreator;
-        deleteBtn.title = isCreator ? '' : `Nur ${incident.created_by_username} kann diese Lage löschen`;
+        deleteBtn.title = isCreator ? '' : `Nur ${(incident.created_by_username || '').split('@')[0]} kann diese Lage löschen`;
 
         // Zusammenfassung mit Quellenverzeichnis
         const summaryText = document.getElementById('summary-text');