feat: Refactor provisioning to instance requests and enhance subdomain availability check

Website/templates/schnell_buchung.html

@@ -208,6 +208,7 @@
                 <div class="booking-review__field">
                     <label for="school_name">Schule/Einrichtung *</label>
                     <input id="school_name" name="school_name" type="text" required maxlength="160" value="{{ form_data.school_name }}">
+                    <div id="school_name_feedback" style="margin-top:0.4rem; font-size:0.9rem; color:#6b6b6b;"></div>
                 </div>
                 <div class="booking-review__field">
                     <label for="contact_email">E-Mail *</label>
@@ -242,10 +243,54 @@
             </div>
 
             <div class="booking-review__actions">
-                <button class="btn" type="submit">{{ confirm_label }}</button>
+                <button id="booking_submit" class="btn" type="submit">{{ confirm_label }}</button>
                 <a class="btn secondary" href="{{ url_for('preise') }}">Zurück zu den Preisen</a>
             </div>
         </form>
     </div>
 </section>
+<script>
+(() => {
+    const input = document.getElementById('school_name');
+    const feedback = document.getElementById('school_name_feedback');
+    const submit = document.getElementById('booking_submit');
+    let timer = null;
+
+    function setFeedback(text, ok) {
+        feedback.textContent = text;
+        feedback.style.color = ok ? '#1b8a3e' : '#b02a37';
+        submit.disabled = !ok;
+    }
+
+    async function check(name) {
+        if (!name || name.trim().length < 3) {
+            feedback.textContent = '';
+            submit.disabled = false;
+            return;
+        }
+        try {
+            const params = new URLSearchParams({ school_name: name });
+            const res = await fetch(`/instance_request/check_subdomain?${params.toString()}`, { credentials: 'same-origin' });
+            if (!res.ok) throw new Error('Netzwerkfehler');
+            const j = await res.json();
+            setFeedback(j.message || (j.available ? 'verfügbar' : 'nicht verfügbar'), !!j.available);
+        } catch (e) {
+            setFeedback('Prüfung fehlgeschlagen (Netzwerk).', false);
+        }
+    }
+
+    if (input) {
+        input.addEventListener('input', (e) => {
+            clearTimeout(timer);
+            const val = e.target.value;
+            timer = setTimeout(() => check(val), 500);
+        });
+
+        // initial check on load
+        if (input.value && input.value.trim()) {
+            check(input.value);
+        }
+    }
+})();
+</script>
 {% endblock %}