fix(a11y): WCAG 2 AA contrast, labels and dropdown

lib/mv_web/components/core_components.ex

@@ -562,13 +562,17 @@ defmodule MvWeb.CoreComponents do
                 phx-target={@phx_target}
               >
                 <%= if @checkboxes do %>
-                  <input
-                    type="checkbox"
-                    checked={Map.get(@selected, item.value, true)}
-                    class="checkbox checkbox-sm checkbox-primary pointer-events-none"
-                    tabindex="-1"
+                  <%!-- Visual-only indicator: do not nest an interactive control (checkbox) inside the button for screen reader and focus correctness (WCAG 2.1.2). --%>
+                  <span
+                    class={
+                      if Map.get(@selected, item.value, true),
+                        do: "text-primary",
+                        else: "text-base-300"
+                    }
                     aria-hidden="true"
-                  />
+                  >
+                    <.icon name="hero-check" class="size-4 shrink-0" />
+                  </span>
                 <% end %>
                 <span>{item.label}</span>
               </button>