fix: improve accent color contrast for WCAG AA compliance

Add WCAG AA compliant accent color variants and update default accent
to meet 4.5:1 contrast ratio requirements.

- Add --t-accent-text (darker for text on light backgrounds)
- Add --t-accent-button (darker for button backgrounds with white text)
- Change default accent from #3b82f6 to #2563eb (better contrast)
- Update presets and tests for new default

These changes ensure accent colors meet accessibility standards while
maintaining visual consistency with the brand palette.

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

assets/css/theme-semantic.css

@@ -23,6 +23,12 @@
   --t-accent-subtle: hsl(var(--t-accent-h) 40% 95%);
   --t-accent-ring: hsl(var(--t-accent-h) var(--t-accent-s) var(--t-accent-l) / 0.4);
 
+  /* WCAG AA compliant accent variants for better contrast */
+  /* Darker accent for text on light backgrounds (4.5:1 with white) */
+  --t-accent-text: hsl(var(--t-accent-h) var(--t-accent-s) 38%);
+  /* Darker accent for button backgrounds to ensure 4.5:1 with white text */
+  --t-accent-button: hsl(var(--t-accent-h) var(--t-accent-s) 42%);
+
   /* Secondary colors */
   --t-secondary-accent: #ea580c;
   --t-sale-color: #dc2626;

lib/simpleshop_theme/theme/presets.ex

@@ -23,7 +23,7 @@ defmodule SimpleshopTheme.Theme.Presets do
       density: "balanced",
       grid_columns: "4",
       header_layout: "standard",
-      accent_color: "#3b82f6",
+      accent_color: "#2563eb",
       layout_width: "wide",
       card_shadow: "sm",
       announcement_bar: true

test/simpleshop_theme/settings_test.exs

@@ -124,7 +124,7 @@ defmodule SimpleshopTheme.SettingsTest do
       {:ok, settings} = Settings.apply_preset(:studio)
       assert settings.mood == "neutral"
       assert settings.typography == "clean"
-      assert settings.accent_color == "#3b82f6"
+      assert settings.accent_color == "#2563eb"
     end
 
     test "returns error for invalid preset" do

test/simpleshop_theme/theme/presets_test.exs

@@ -42,7 +42,7 @@ defmodule SimpleshopTheme.Theme.PresetsTest do
       assert preset.density == "balanced"
       assert preset.grid_columns == "4"
       assert preset.header_layout == "standard"
-      assert preset.accent_color == "#3b82f6"
+      assert preset.accent_color == "#2563eb"
     end
 
     test "returns boutique preset" do