feat: fixed footer with responsive height tokens

Footer is fixed bottom-0 with h-footer (5rem mobile) / md:h-footer-wide
(4rem desktop). Body gets matching pb-footer/md:pb-footer-wide to
reserve space. Tokens registered in @theme inline as --spacing-footer*.

src/shared/styles/theme.css

@@ -84,7 +84,6 @@
   /* === GRID === */
   --grid-gap: var(--space-3);
   --section-content-width: 72rem;
-
   /* === ANIMATION === */
   --ease-default: ease;
   --ease-spring: cubic-bezier(0.34, 1.56, 0.64, 1);
@@ -121,6 +120,8 @@
   --radius-md: var(--radius);
   --radius-lg: var(--radius);
   --container-section: var(--section-content-width);
+  --spacing-footer: 5rem;
+  --spacing-footer-wide: 4rem;
   --text-section-title: var(--text-section-title);
 
   --shadow-brutal-xs: var(--shadow-brutal-xs);
@@ -226,12 +227,6 @@
   a {
     color: var(--blue);
     text-decoration: none;
-    border-bottom: 2px solid var(--blue);
-    transition: all 0.2s;
-  }
-
-  a:hover {
-    border-bottom-width: 4px;
   }
 
   blockquote {
@@ -258,19 +253,19 @@
 .brutal-shadow-lg {
   box-shadow: var(--shadow-brutal-lg);
 }
-.brutal-border {
+@utility brutal-border {
   border: var(--border-width) solid var(--blue);
 }
-.brutal-border-top {
+@utility brutal-border-top {
   border-top: var(--border-width) solid var(--blue);
 }
-.brutal-border-bottom {
+@utility brutal-border-bottom {
   border-bottom: var(--border-width) solid var(--blue);
 }
-.brutal-border-left {
+@utility brutal-border-left {
   border-left: var(--border-width) solid var(--blue);
 }
-.brutal-border-right {
+@utility brutal-border-right {
   border-right: var(--border-width) solid var(--blue);
 }
 /* Apply Fraunces variable axes to non-heading elements using the heading font */
@@ -300,6 +295,16 @@
   text-wrap: pretty;
 }
 
+.rich-text a {
+  border-bottom: var(--border-width) solid var(--blue);
+  opacity: 1;
+  transition: opacity var(--duration-normal);
+}
+
+.rich-text a:hover {
+  opacity: 0.6;
+}
+
 .rich-text p + p {
   margin-top: 1.2em;
 }