fix: move templates to root directory for Flask discovery

app/templates/register.html

@@ -1,12 +0,0 @@
-{% extends "base.html" %}
-{% block content %}
-<h2>Registrieren</h2>
-<form method="post">
-    <label>Benutzername</label>
-    <input type="text" name="username" required>
-    <label>Passwort</label>
-    <input type="password" name="password" required>
-    <button type="submit" class="btn btn-primary">Registrieren</button>
-</form>
-<p style="margin-top:1rem;">Bereits registriert? <a href="{{ url_for('login') }}">Anmelden</a></p>
-{% endblock %}