add header background contrast warning and improve branding UX

- extract dominant colors from header images during optimization
- calculate WCAG contrast ratios against theme text color
- show warning in theme editor when text may be hard to read
- prevent hiding shop name when no logo is uploaded
- auto-enable shop name when logo is deleted
- fix image cache invalidation on delete
- add missing .hidden utility class

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/berrypod_web/components/shop_components/layout.ex

@@ -929,41 +929,32 @@ defmodule BerrypodWeb.ShopComponents.Layout do
   attr :logo_image, :map, default: nil
 
   defp logo_inner(assigns) do
+    # Show logo if enabled and image exists
+    show_logo = assigns.theme_settings.show_logo && assigns.logo_image
+
+    # Show site name if enabled, or as fallback when logo should show but image is missing
+    show_site_name =
+      assigns.theme_settings.show_site_name ||
+        (assigns.theme_settings.show_logo && !assigns.logo_image)
+
+    assigns =
+      assigns
+      |> assign(:show_logo, show_logo)
+      |> assign(:show_site_name, show_site_name)
+
     ~H"""
-    <%= case @theme_settings.logo_mode do %>
-      <% "text-only" -> %>
-        <span class="shop-logo-text">
-          {@site_name}
-        </span>
-      <% "logo-text" -> %>
-        <%= if @logo_image do %>
-          <img
-            src={logo_url(@logo_image, @theme_settings)}
-            alt={@site_name}
-            class="shop-logo-img"
-            style={"height: #{@theme_settings.logo_size}px;"}
-          />
-        <% end %>
-        <span class="shop-logo-text">
-          {@site_name}
-        </span>
-      <% "logo-only" -> %>
-        <%= if @logo_image do %>
-          <img
-            src={logo_url(@logo_image, @theme_settings)}
-            alt={@site_name}
-            class="shop-logo-img"
-            style={"height: #{@theme_settings.logo_size}px;"}
-          />
-        <% else %>
-          <span class="shop-logo-text">
-            {@site_name}
-          </span>
-        <% end %>
-      <% _ -> %>
-        <span class="shop-logo-text">
-          {@site_name}
-        </span>
+    <%= if @show_logo do %>
+      <img
+        src={logo_url(@logo_image, @theme_settings)}
+        alt={@site_name}
+        class="shop-logo-img"
+        style={"height: #{@theme_settings.logo_size}px;"}
+      />
+    <% end %>
+    <%= if @show_site_name do %>
+      <span class="shop-logo-text">
+        {@site_name}
+      </span>
     <% end %>
     """
   end