Add multi account support to shpping cart

src/allmende_payment_system/templates/order.html.jinja

@@ -70,8 +70,20 @@
 
         {% if is_cart %}
         <div class="d-flex justify-content-between align-items-center mt-3">
-            <div>
-                <a href="/shop/finalize_order" class="btn btn-primary">Jetzt Buchen</a>
+            <div    >
+                <form method="post" action="/shop/finalize_order" class="d-flex align-items-center">
+                    {% if user.accounts|length > 1 %}
+                        <select name="account_id" class="form-select form-select-sm me-2" required>
+                            <option value="">-- Konto wählen --</option>
+                            {% for account in user.accounts %}
+                                <option value="{{ account.id }}">{{ account.name }} ({{ account.balance | format_number }} €)</option>
+                            {% endfor %}
+                        </select>
+                    {% elif user.accounts|length == 1 %}
+                        <input type="hidden" name="account_id" value="{{ user.accounts[0].id }}">
+                    {% endif %}
+                    <button type="submit" class="btn btn-primary">Jetzt Bezahlen</button>
+                </form>
             </div>
         </div>
         {% endif %}