feat(design): add typography utilities (typography.css)

Change-Id: Ifc25f727b3c5030d85a093da93a33fac546cb23e

Author: jd

src/styles/typography.css

@@ -0,0 +1,62 @@
+/*
+  Typography utilities. Apply by class on custom-built pages.
+  MDX-rendered headings inherit the same properties via #main-content
+  selectors in index.css (kept in sync — see DESIGN.md).
+*/
+
+.heading-hero {
+  font-size: clamp(2.5rem, 4.5vw, 3rem);
+  font-weight: 500;
+  line-height: 1.2;
+  letter-spacing: -0.025em;
+  text-wrap: balance;
+}
+
+.heading-page {
+  font-size: 2rem;
+  font-weight: 500;
+  line-height: 1.2;
+  letter-spacing: -0.025em;
+  text-wrap: balance;
+}
+
+.heading-section {
+  font-size: 1.5rem;
+  font-weight: 500;
+  line-height: 1.3;
+  letter-spacing: -0.025em;
+  text-wrap: balance;
+}
+
+.heading-subsection {
+  font-size: 1.25rem;
+  font-weight: 500;
+  line-height: 1.3;
+  letter-spacing: -0.01em;
+}
+
+.heading-detail {
+  font-size: 1.125rem;
+  font-weight: 500;
+  line-height: 1.4;
+}
+
+.heading-minor {
+  font-size: 1rem;
+  font-weight: 500;
+  line-height: 1.4;
+}
+
+.text-subtitle {
+  font-size: 1.125rem;
+  font-weight: 400;
+  line-height: 1.5;
+  text-wrap: balance;
+}
+
+.text-eyebrow {
+  font-size: 0.75rem;
+  font-weight: 600;
+  letter-spacing: 0.1em;
+  text-transform: uppercase;
+}