fix: brand contrast — chick-only header mark, ink callouts, nav polish

Phase 1 brand palette reused --c-sky for both the header background and
the word "Babies" inside the logo art, erasing it visually. Same class
of problem hit the contact page mailto callout.

- Split logo into chick mark + HTML site title so the wordmark colors
  no longer need to coexist with the header surface. Generator gains
  build_logo_mark_{png,webp} with a widest-gap column scan to crop.
- Header moves to --c-wheat; nav active state flips to ink pill with
  cream text; muted Shop link reads as coming-soon (italic + dim +
  not-allowed).
- Contact page mailto callout reskinned to ink/cream (strong CTA) and
  form note shifts from pale sky-deep to ink at 70% opacity.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/templates/public/base.html

@@ -34,14 +34,17 @@
   <header class="site-header">
     <div class="wrap site-header__wrap">
       <a class="site-header__brand" href="/" aria-label="Chicken Babies R Us home">
-        {# WebP with PNG fallback — generated by scripts/generate_static_assets.py. #}
+        {# Chick-only mark paired with the site title as styled text.
+           Decoupling the mark from the wordmark lets the header colors
+           change freely without the multi-colored logo text clashing. #}
         <picture>
-          <source srcset="{{ url_for('static', path='img/logo.webp') }}" type="image/webp">
-          <img src="{{ url_for('static', path='img/logo.png') }}"
-               alt="Chicken Babies R Us"
-               height="48"
-               class="site-header__logo">
+          <source srcset="{{ url_for('static', path='img/logo-mark.webp') }}" type="image/webp">
+          <img src="{{ url_for('static', path='img/logo-mark.png') }}"
+               alt=""
+               height="56"
+               class="site-header__mark">
         </picture>
+        <span class="site-header__title">Chicken Babies R Us</span>
       </a>
 
       {# The mobile toggle button — script below attaches a click handler