feat: add theme selector to unauthenticated pages

lib/mv_web/components/core_components.ex

@@ -1295,6 +1295,41 @@ defmodule MvWeb.CoreComponents do
     """
   end
 
+  @doc """
+  Renders a theme toggle using DaisyUI swap (sun/moon with rotate effect).
+
+  Wired to the theme script in root layout: checkbox uses `data-theme-toggle`,
+  root script syncs checked state (checked = dark) and listens for `phx:set-theme`.
+  Use in public header or sidebar. Optional `class` is applied to the wrapper.
+  """
+  attr :class, :string, default: nil, doc: "Optional extra classes for the swap wrapper"
+
+  def theme_swap(assigns) do
+    assigns = assign(assigns, :wrapper_class, assigns[:class])
+
+    ~H"""
+    <div class={[@wrapper_class]}>
+      <label
+        class="swap swap-rotate cursor-pointer focus-within:outline-none focus-within:focus-visible:ring-2 focus-within:focus-visible:ring-primary focus-within:focus-visible:ring-offset-2 rounded"
+        aria-label={gettext("Toggle dark mode")}
+      >
+        <input
+          type="checkbox"
+          data-theme-toggle
+          aria-label={gettext("Toggle dark mode")}
+          onchange="window.dispatchEvent(new CustomEvent('phx:set-theme',{detail:{theme:this.checked?'dark':'light'}}))"
+        />
+        <span class="swap-on size-6 flex items-center justify-center" aria-hidden="true">
+          <.icon name="hero-moon" class="size-5" />
+        </span>
+        <span class="swap-off size-6 flex items-center justify-center" aria-hidden="true">
+          <.icon name="hero-sun" class="size-5" />
+        </span>
+      </label>
+    </div>
+    """
+  end
+
   @doc """
   Renders a [Heroicon](https://heroicons.com).