feat(admin): replace browser confirm() dialogs with native <dialog> modal

- Add styled <dialog id="confirm-dialog"> to base_admin.html — frosted
  backdrop, rounded card, Cancel / Confirm buttons
- Add confirmAction(message, form) JS helper — clones OK button to
  avoid listener accumulation, calls form.submit() on confirm
- Replace all 5 onclick="return confirm()" across templates with
  type="button" + confirmAction(..., this.closest('form'))
  · articles.html — Rebuild All
  · template_detail.html — Regenerate
  · generate_form.html — Generate Articles
  · scenario_results.html — Delete scenario
  · audience_contacts.html — Remove contact

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/src/padelnomics/admin/templates/admin/articles.html

@@ -18,7 +18,7 @@
       <a href="{{ url_for('admin.article_new') }}" class="btn btn-sm">New Article</a>
       <form method="post" action="{{ url_for('admin.rebuild_all') }}" class="m-0" style="display:inline">
         <input type="hidden" name="csrf_token" value="{{ csrf_token() }}">
-        <button type="submit" class="btn-outline btn-sm" onclick="return confirm('Rebuild all articles?')">Rebuild All</button>
+        <button type="button" class="btn-outline btn-sm" onclick="confirmAction('Rebuild all articles? This will re-render every article from its template.', this.closest('form'))">Rebuild All</button>
       </form>
     </div>
   </header>

web/src/padelnomics/admin/templates/admin/audience_contacts.html

@@ -30,7 +30,7 @@
             <form method="post" action="{{ url_for('admin.audience_contact_remove', audience_id=audience.audience_id) }}" style="display:inline">
               <input type="hidden" name="csrf_token" value="{{ csrf_token() }}">
               <input type="hidden" name="contact_id" value="{{ c.id if c.id is defined else (c.get('id', '') if c is mapping else '') }}">
-              <button type="submit" class="btn-outline btn-sm" style="color:#DC2626" onclick="return confirm('Remove this contact?')">Remove</button>
+              <button type="button" class="btn-outline btn-sm" style="color:#DC2626" onclick="confirmAction('Remove this contact from the audience?', this.closest('form'))">Remove</button>
             </form>
           </td>
         </tr>

web/src/padelnomics/admin/templates/admin/base_admin.html

@@ -27,6 +27,14 @@
 
   .admin-main { flex: 1; padding: 2rem; overflow-y: auto; }
 
+  #confirm-dialog {
+    border: none; border-radius: 12px; padding: 1.5rem; max-width: 380px; width: 90%;
+    box-shadow: 0 20px 60px rgba(0,0,0,0.15), 0 4px 16px rgba(0,0,0,0.08);
+  }
+  #confirm-dialog::backdrop { background: rgba(15,23,42,0.45); backdrop-filter: blur(3px); }
+  #confirm-dialog p { margin: 0 0 1.25rem; font-size: 0.9375rem; color: #0F172A; line-height: 1.55; }
+  #confirm-dialog .dialog-actions { display: flex; gap: 0.5rem; justify-content: flex-end; }
+
   @media (max-width: 768px) {
     .admin-layout { flex-direction: column; }
     .admin-sidebar {
@@ -130,4 +138,24 @@
     {% block admin_content %}{% endblock %}
   </main>
 </div>
+
+<dialog id="confirm-dialog">
+  <p id="confirm-msg"></p>
+  <div class="dialog-actions">
+    <button id="confirm-cancel" class="btn-outline btn-sm">Cancel</button>
+    <button id="confirm-ok" class="btn btn-sm">Confirm</button>
+  </div>
+</dialog>
+<script>
+function confirmAction(message, form) {
+  var dialog = document.getElementById('confirm-dialog');
+  document.getElementById('confirm-msg').textContent = message;
+  var ok = document.getElementById('confirm-ok');
+  var newOk = ok.cloneNode(true);
+  ok.replaceWith(newOk);
+  newOk.addEventListener('click', function() { dialog.close(); form.submit(); });
+  document.getElementById('confirm-cancel').addEventListener('click', function() { dialog.close(); }, { once: true });
+  dialog.showModal();
+}
+</script>
 {% endblock %}

web/src/padelnomics/admin/templates/admin/generate_form.html

@@ -45,7 +45,7 @@
         </p>
       </div>
 
-      <button type="submit" class="btn" style="width: 100%;" onclick="return confirm('Generate articles? Existing articles will be updated.')">
+      <button type="button" class="btn" style="width: 100%;" onclick="confirmAction('Generate articles? Existing articles will be updated in-place.', this.closest('form'))">
         Generate Articles
       </button>
     </form>

web/src/padelnomics/admin/templates/admin/partials/scenario_results.html

@@ -32,7 +32,7 @@
         <a href="{{ url_for('admin.scenario_edit', scenario_id=s.id) }}" class="btn-outline btn-sm">Edit</a>
         <form method="post" action="{{ url_for('admin.scenario_delete', scenario_id=s.id) }}" class="m-0" style="display: inline;">
           <input type="hidden" name="csrf_token" value="{{ csrf_token() }}">
-          <button type="submit" class="btn-outline btn-sm" onclick="return confirm('Delete this scenario?')">Delete</button>
+          <button type="button" class="btn-outline btn-sm" onclick="confirmAction('Delete this scenario? This cannot be undone.', this.closest('form'))">Delete</button>
         </form>
       </td>
     </tr>

web/src/padelnomics/admin/templates/admin/template_detail.html

@@ -15,7 +15,7 @@
       <a href="{{ url_for('admin.template_generate', slug=config_data.slug) }}" class="btn">Generate Articles</a>
       <form method="post" action="{{ url_for('admin.template_regenerate', slug=config_data.slug) }}" style="display:inline">
         <input type="hidden" name="csrf_token" value="{{ csrf_token() }}">
-        <button type="submit" class="btn-outline" onclick="return confirm('Regenerate all articles for this template with fresh data?')">
+        <button type="button" class="btn-outline" onclick="confirmAction('Regenerate all articles for this template with fresh data? Existing articles will be overwritten.', this.closest('form'))">
           Regenerate
         </button>
       </form>