perf: improve SEO and accessibility for PageSpeed

- Add meta description tag with theme_settings.site_description fallback
- Add site_description field to ThemeSettings schema
- Fix color contrast on tertiary text (WCAG AA compliance)
  - Clean mood: #a3a3a3 → #737373
  - Warm mood: #a8a29e → #78716c
  - Cool mood: #94a3b8 → #64748b
- Add width/height attributes to product images to prevent CLS:
  - Product cards: 600x600
  - Cart items: 96x96
  - Gallery thumbnails: 150x150
  - Lightbox: 1200x1200

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

lib/simpleshop_theme/settings/theme_settings.ex

@@ -16,6 +16,7 @@ defmodule SimpleshopTheme.Settings.ThemeSettings do
 
     # Branding
     field :site_name, :string, default: "Store Name"
+    field :site_description, :string, default: "Discover unique products and original designs."
     field :logo_mode, :string, default: "text-only"
     field :logo_image_id, :binary_id
     field :logo_size, :integer, default: 36
@@ -62,6 +63,7 @@ defmodule SimpleshopTheme.Settings.ThemeSettings do
       :header_layout,
       :accent_color,
       :site_name,
+      :site_description,
       :logo_mode,
       :logo_image_id,
       :logo_size,

lib/simpleshop_theme/theme/css_generator.ex

@@ -58,7 +58,7 @@ defmodule SimpleshopTheme.Theme.CSSGenerator do
       --t-surface-overlay: rgba(255, 255, 255, 0.95);
       --t-text-primary: #171717;
       --t-text-secondary: #525252;
-      --t-text-tertiary: #a3a3a3;
+      --t-text-tertiary: #737373;
       --t-text-inverse: #ffffff;
       --t-border-default: #e5e5e5;
       --t-border-subtle: #f0f0f0;
@@ -73,7 +73,7 @@ defmodule SimpleshopTheme.Theme.CSSGenerator do
       --t-surface-overlay: rgba(253, 248, 243, 0.95);
       --t-text-primary: #1c1917;
       --t-text-secondary: #57534e;
-      --t-text-tertiary: #a8a29e;
+      --t-text-tertiary: #78716c;
       --t-text-inverse: #ffffff;
       --t-border-default: #e7e0d8;
       --t-border-subtle: #f0ebe4;
@@ -88,7 +88,7 @@ defmodule SimpleshopTheme.Theme.CSSGenerator do
       --t-surface-overlay: rgba(244, 247, 251, 0.95);
       --t-text-primary: #0f172a;
       --t-text-secondary: #475569;
-      --t-text-tertiary: #94a3b8;
+      --t-text-tertiary: #64748b;
       --t-text-inverse: #ffffff;
       --t-border-default: #d4dce8;
       --t-border-subtle: #e8eff5;

lib/simpleshop_theme_web/components/layouts/shop_root.html.heex

@@ -4,6 +4,7 @@
     <meta charset="utf-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1" />
     <meta name="csrf-token" content={get_csrf_token()} />
+    <meta name="description" content={assigns[:page_description] || @theme_settings.site_description || "Welcome to #{@theme_settings.site_name}"} />
     <.live_title><%= assigns[:page_title] || @theme_settings.site_name %></.live_title>
     <link phx-track-static rel="stylesheet" href={~p"/assets/css/app.css"} />
     <script defer phx-track-static type="text/javascript" src={~p"/assets/js/app.js"}>

lib/simpleshop_theme_web/components/shop_components.ex

@@ -860,6 +860,8 @@ defmodule SimpleshopThemeWeb.ShopComponents do
       <img
         src={@product.image_url}
         alt={@product.name}
+        width="600"
+        height="600"
         loading={if @variant == :minimal, do: nil, else: "lazy"}
         decoding={if @variant == :minimal, do: nil, else: "async"}
         class="product-image-primary w-full h-full object-cover transition-opacity duration-300"
@@ -868,6 +870,8 @@ defmodule SimpleshopThemeWeb.ShopComponents do
         <img
           src={@product.hover_image_url}
           alt={@product.name}
+          width="600"
+          height="600"
           loading={if @variant == :minimal, do: nil, else: "lazy"}
           decoding={if @variant == :minimal, do: nil, else: "async"}
           class="product-image-hover w-full h-full object-cover"
@@ -2255,6 +2259,9 @@ defmodule SimpleshopThemeWeb.ShopComponents do
         <img
           src={@item.product.image_url}
           alt={@item.product.name}
+          width="96"
+          height="96"
+          loading="lazy"
           class="w-full h-full object-cover"
         />
       </div>
@@ -2696,6 +2703,8 @@ defmodule SimpleshopThemeWeb.ShopComponents do
           id={"#{@id_prefix}-main-image"}
           src={List.first(@images)}
           alt={@product_name}
+          width="600"
+          height="600"
           class="w-full h-full object-cover"
         />
         <div class="absolute inset-0 flex items-center justify-center opacity-0 hover:opacity-100 transition-opacity bg-black/10">
@@ -2721,6 +2730,9 @@ defmodule SimpleshopThemeWeb.ShopComponents do
             <img
               src={img_url}
               alt={@product_name}
+              width="150"
+              height="150"
+              loading="lazy"
               class="w-full h-full object-cover"
             />
           </button>
@@ -2787,6 +2799,8 @@ defmodule SimpleshopThemeWeb.ShopComponents do
               id="lightbox-image"
               src={List.first(@images)}
               alt={@product_name}
+              width="1200"
+              height="1200"
             />
           </div>
           <figcaption class="lightbox-caption"><%= @product_name %></figcaption>