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/routers/incidents.py

@@ -55,14 +55,14 @@ async def _enrich_incident(db: aiosqlite.Connection, row: aiosqlite.Row) -> dict
     source_count = (await cursor.fetchone())["cnt"]
 
     cursor = await db.execute(
-        "SELECT username FROM users WHERE id = ?",
+        "SELECT email FROM users WHERE id = ?",
         (incident["created_by"],),
     )
     user_row = await cursor.fetchone()
 
     incident["article_count"] = article_count
     incident["source_count"] = source_count
-    incident["created_by_username"] = user_row["username"] if user_row else "Unbekannt"
+    incident["created_by_username"] = user_row["email"] if user_row else "Unbekannt"
     return incident
 
 
@@ -744,9 +744,9 @@ async def export_incident(
     incident = dict(row)
 
     # Ersteller-Name
-    cursor = await db.execute("SELECT username FROM users WHERE id = ?", (incident["created_by"],))
+    cursor = await db.execute("SELECT email FROM users WHERE id = ?", (incident["created_by"],))
     user_row = await cursor.fetchone()
-    creator = user_row["username"] if user_row else "Unbekannt"
+    creator = user_row["email"] if user_row else "Unbekannt"
 
     # Artikel
     cursor = await db.execute(