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/models/user.py

@@ -9,6 +9,8 @@ class User(db.Model):
     id = db.Column(db.Integer, primary_key=True)
     username = db.Column(db.String(80), unique=True, nullable=False, index=True)
     email = db.Column(db.String(255), unique=True, nullable=True)
+    first_name = db.Column(db.String(100), nullable=True)
+    last_name = db.Column(db.String(100), nullable=True)
     password_hash = db.Column(db.String(255), nullable=False)
     role = db.Column(db.String(20), default='user', nullable=False)  # 'admin' or 'user'
     master_key_salt = db.Column(db.LargeBinary, nullable=True)  # For password manager
@@ -23,6 +25,7 @@ class User(db.Model):
                             foreign_keys='File.owner_id')
     calendars = db.relationship('Calendar', backref='owner', lazy='dynamic')
     address_books = db.relationship('AddressBook', backref='owner', lazy='dynamic')
+    task_lists = db.relationship('TaskList', backref='owner', lazy='dynamic')
     email_accounts = db.relationship('EmailAccount', backref='user', lazy='dynamic',
                                      order_by='EmailAccount.sort_order')
     password_folders = db.relationship('PasswordFolder', backref='owner', lazy='dynamic')
@@ -33,10 +36,25 @@ class User(db.Model):
     def check_password(self, password):
         return bcrypt.check_password_hash(self.password_hash, password)
 
+    @property
+    def full_name(self) -> str:
+        """Vor- + Nachname zusammengesetzt, sonst Leerstring."""
+        parts = [self.first_name or '', self.last_name or '']
+        return ' '.join(p.strip() for p in parts if p and p.strip())
+
+    @property
+    def display_name(self) -> str:
+        """Voller Name falls vorhanden, sonst Username."""
+        return self.full_name or self.username
+
     def to_dict(self, include_email=False):
         data = {
             'id': self.id,
             'username': self.username,
+            'first_name': self.first_name or '',
+            'last_name': self.last_name or '',
+            'full_name': self.full_name,
+            'display_name': self.display_name,
             'role': self.role,
             'is_active': self.is_active,
             'storage_quota_mb': self.storage_quota_mb,