feat: conistent danger zone delete flow

lib/mv_web/live/group_live/form.ex

@@ -101,6 +101,31 @@ defmodule MvWeb.GroupLive.Form do
               rows="4"
             />
           </div>
+
+          <%!-- Danger zone: canonical pattern (same as member form) --%>
+          <%= if @group && can?(@current_user, :destroy, @group) do %>
+            <section class="mt-8 mb-6" aria-labelledby="danger-zone-heading">
+              <h2 id="danger-zone-heading" class="text-lg font-semibold mb-3 text-error">
+                {gettext("Danger zone")}
+              </h2>
+              <div class="border border-base-300 rounded-lg p-4 bg-base-100">
+                <p class="text-base-content/70 mb-4">
+                  {gettext(
+                    "Deleting this group cannot be undone. All member-group associations will be permanently removed."
+                  )}
+                </p>
+                <.button
+                  variant="danger"
+                  navigate={~p"/groups/#{@group.slug}?confirm_delete=1"}
+                  data-testid="group-form-delete-btn"
+                  aria-label={gettext("Delete group %{name}", name: @group.name)}
+                >
+                  <.icon name="hero-trash" class="size-4" />
+                  {gettext("Delete group")}
+                </.button>
+              </div>
+            </section>
+          <% end %>
         </div>
       </.form>
     </Layouts.app>