feat: Vor-/Nachname, geteilte Listen zeigen Eigentuemer

Backend:
- User.first_name / User.last_name (nullable, Auto-Migrate fuegt sie an)
  full_name/display_name als Properties + in to_dict
- TaskList.owner-Relationship ergaenzt (fehlte, daher wurden geteilte
  Listen beim Empfaenger nicht korrekt aufgeloest)
- /auth/me GET + PUT (Profil bearbeiten: Vorname, Nachname, E-Mail)
- /users/search findet jetzt auch nach Vor-/Nachname und liefert
  full_name/display_name mit
- list_tasklists/list_calendars/list_addressbooks liefern
  owner_full_name und owner_display_name

Frontend:
- Sidebars bei Kontakten/Kalender/Aufgaben: "(geteilt von <Voller Name>)"
  mit Fallback auf Username
- User-Search-Popup zeigt vollen Namen neben Username
- SettingsView: Vorname/Nachname/E-Mail bearbeiten

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

backend/app/api/users.py

@@ -281,6 +281,31 @@ def create_invite_link():
 
 # --- User search (for sharing dialogs) ---
 
+@api_bp.route('/auth/me', methods=['GET'])
+@token_required
+def get_me():
+    return jsonify(request.current_user.to_dict(include_email=True)), 200
+
+
+@api_bp.route('/auth/me', methods=['PUT'])
+@token_required
+def update_me():
+    user = request.current_user
+    data = request.get_json() or {}
+    if 'first_name' in data:
+        user.first_name = (data.get('first_name') or '').strip() or None
+    if 'last_name' in data:
+        user.last_name = (data.get('last_name') or '').strip() or None
+    if 'email' in data:
+        email = (data.get('email') or '').strip() or None
+        if email and email != user.email:
+            if User.query.filter(User.email == email, User.id != user.id).first():
+                return jsonify({'error': 'E-Mail ist bereits vergeben'}), 409
+        user.email = email
+    db.session.commit()
+    return jsonify(user.to_dict(include_email=True)), 200
+
+
 @api_bp.route('/users/search', methods=['GET'])
 @token_required
 def search_users():
@@ -289,13 +314,19 @@ def search_users():
     if len(query) < 2:
         return jsonify([]), 200
 
+    like = f'%{query}%'
     users = User.query.filter(
-        User.username.ilike(f'%{query}%'),
+        (User.username.ilike(like)) | (User.first_name.ilike(like)) | (User.last_name.ilike(like)),
         User.id != request.current_user.id,
         User.is_active == True,
     ).limit(10).all()
 
-    return jsonify([{'id': u.id, 'username': u.username} for u in users]), 200
+    return jsonify([{
+        'id': u.id,
+        'username': u.username,
+        'full_name': u.full_name,
+        'display_name': u.display_name,
+    } for u in users]), 200
 
 
 # --- Change password (non-admin, own account) ---