fix: disable public signup and restore local login flow

app/routes/auth.py

@@ -11,6 +11,10 @@ from ..models import User
 bp = Blueprint("auth", __name__)
 
 
+def registration_open() -> bool:
+    return User.query.count() == 0
+
+
 @bp.route("/login", methods=["GET", "POST"])
 def login():
     if current_user.is_authenticated:
@@ -24,13 +28,16 @@ def login():
             flash(f"Willkommen zurück, {user.name}.", "success")
             return redirect(url_for("tasks.my_tasks"))
         flash("Die Kombination aus E-Mail und Passwort passt leider nicht.", "error")
-    return render_template("auth/login.html", form=form)
+    return render_template("auth/login.html", form=form, registration_open=registration_open())
 
 
 @bp.route("/register", methods=["GET", "POST"])
 def register():
     if current_user.is_authenticated:
         return redirect(url_for("tasks.my_tasks"))
+    if not registration_open():
+        flash("Freie Registrierung ist deaktiviert.", "info")
+        return redirect(url_for("auth.login"))
 
     form = RegisterForm()
     if form.validate_on_submit():
@@ -50,4 +57,3 @@ def logout():
     logout_user()
     flash("Du bist jetzt abgemeldet.", "info")
     return redirect(url_for("auth.login"))
-