feat: replace fetch-based modal forms with Turbo Frames (#181)

Enable @hotwired/turbo with Drive explicitly disabled, then migrate the
bo--modal-form Stimulus controller (custom fetch + X-Modal-Request pattern)
to a thin bo--modal controller that lets Turbo handle HTTP and DOM swap.
Adds frame templates for quiz questions and bank questions; controllers now
detect Turbo-Frame header instead of X-Modal-Request.

templates/backoffice/quiz/_question_detail_frame.html.twig

@@ -0,0 +1,23 @@
+<turbo-frame id="question-modal-frame">
+    <div class="modal-body">
+        <p class="fw-semibold mb-3">{{ question.question }}</p>
+        <ul class="list-group">
+            {% for answer in question.answers %}
+                <li class="list-group-item d-flex justify-content-between align-items-center">
+                    <span{% if answer.isRightAnswer %} class="fw-semibold"{% endif %}>
+                        {% if answer.isRightAnswer %}<i class="bi bi-check-circle-fill text-success me-1"></i>{% endif %}
+                        {{ answer.text }}
+                    </span>
+                    {% if answer.candidates|length > 0 %}
+                        <span class="text-muted small">{{ answer.candidates|map(c => c.name)|join(', ') }}</span>
+                    {% endif %}
+                </li>
+            {% else %}
+                <li class="list-group-item text-muted">{{ 'There are no answers for this question'|trans }}</li>
+            {% endfor %}
+        </ul>
+    </div>
+    <div class="modal-footer">
+        <button type="button" class="btn btn-secondary" data-bs-dismiss="modal">{{ 'Close'|trans }}</button>
+    </div>
+</turbo-frame>