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/static/css/site.css

@@ -158,8 +158,8 @@ a:focus-visible {
 
 /* Header / brand / nav ---------------------------------------------------- */
 .site-header {
-  background-color: var(--c-sky);
-  border-bottom: 1px solid rgba(43, 58, 66, 0.1);
+  background-color: var(--c-wheat);
+  border-bottom: 1px solid rgba(43, 58, 66, 0.15);
 }
 
 .site-header__wrap {
@@ -174,12 +174,30 @@ a:focus-visible {
 .site-header__brand {
   display: inline-flex;
   align-items: center;
+  gap: var(--space-3);
   text-decoration: none;
+  color: var(--c-ink);
 }
 
-.site-header__logo {
-  height: 48px;
+.site-header__mark {
+  height: 56px;
   width: auto;
+  flex-shrink: 0;
+}
+
+.site-header__title {
+  font-family: var(--font-serif);
+  font-weight: 700;
+  font-size: 1.5rem;
+  line-height: 1.1;
+  letter-spacing: 0.01em;
+  color: var(--c-ink);
+}
+
+@media (max-width: 30rem) {
+  .site-header__title {
+    font-size: 1.25rem;
+  }
 }
 
 /* Mobile nav toggle (shown < 48rem, hidden ≥ 48rem). */
@@ -233,22 +251,37 @@ a:focus-visible {
   text-decoration: none;
   color: var(--c-ink);
   font-weight: 600;
+  transition: background-color 120ms ease, color 120ms ease;
 }
 
 .site-nav__link:hover,
 .site-nav__link:focus-visible {
-  background-color: rgba(255, 255, 255, 0.35);
+  background-color: rgba(43, 58, 66, 0.08);
   color: var(--c-ink);
 }
 
 .site-nav__link.is-active {
-  background-color: var(--c-cream);
-  color: var(--c-sky-deep);
+  background-color: var(--c-ink);
+  color: var(--c-cream);
+}
+
+.site-nav__link.is-active:hover,
+.site-nav__link.is-active:focus-visible {
+  background-color: var(--c-ink);
+  color: var(--c-cream);
 }
 
 /* Muted link for not-yet-live destinations (Shop in Phase 1). */
 .site-nav__link.nav--muted {
-  opacity: 0.65;
+  opacity: 0.55;
+  font-style: italic;
+  font-weight: 500;
+}
+
+.site-nav__link.nav--muted:hover,
+.site-nav__link.nav--muted:focus-visible {
+  background-color: transparent;
+  cursor: not-allowed;
 }
 
 /* Main + footer ----------------------------------------------------------- */
@@ -387,16 +420,34 @@ a:focus-visible {
 
 /* Contact form (inert in Phase 1). */
 .contact-mailto {
-  background-color: var(--c-sky);
+  background-color: var(--c-ink);
+  color: var(--c-cream);
   border-radius: var(--radius);
   padding: var(--space-3);
 }
 
+.contact-mailto a {
+  color: var(--c-cream);
+  text-decoration-color: rgba(250, 243, 231, 0.5);
+}
+
+.contact-mailto a:hover,
+.contact-mailto a:focus-visible {
+  color: #ffffff;
+  text-decoration-color: currentColor;
+}
+
 .contact-mailto--muted {
   background-color: var(--c-wheat);
+  color: var(--c-ink);
   font-style: italic;
 }
 
+.contact-mailto--muted a {
+  color: var(--c-ink);
+  text-decoration-color: currentColor;
+}
+
 .contact-form {
   display: grid;
   gap: var(--space-3);
@@ -407,7 +458,8 @@ a:focus-visible {
 .contact-form__note {
   margin-top: var(--space-3);
   font-style: italic;
-  color: var(--c-sky-deep);
+  color: var(--c-ink);
+  opacity: 0.7;
 }
 
 .contact-form__field {