docs: restore the Quantify brand wordmark

docs/site/src/css/custom.css

@@ -2,7 +2,9 @@
  * Erigon brand colors — light and dark theme.
  * Primary: #EF7716 (Erigon Orange), Hover: #D4660F
  * Light bg: #FFFFFF, Dark bg: #0A0A0A
- * Fonts: Montserrat ExtraBold (headings), Nunito Sans (body)
+ * Fonts: Montserrat ExtraBold (headings), Nunito Sans (body),
+ *        Quantify 700 (brand wordmark — navbar title + footer brand, see
+ *        docusaurus-design-spec.md §7 Font Roles)
  */
 
 @font-face {
@@ -37,6 +39,14 @@
   font-display: swap;
 }
 
+@font-face {
+  font-family: 'Quantify';
+  src: url('/fonts/Quantify.woff2') format('woff2');
+  font-weight: 700;
+  font-style: normal;
+  font-display: swap;
+}
+
 :root {
   /* Brand fonts */
   --ifm-font-family-base: 'Nunito Sans', sans-serif;
@@ -214,8 +224,8 @@ html {
 }
 .navbar__title {
   color: var(--ifm-navbar-link-color);
-  font-family: 'Montserrat', sans-serif;
-  font-weight: 800;
+  font-family: 'Quantify', sans-serif;
+  font-weight: 700;
   letter-spacing: 0.04em;
 }
 .navbar .clean-btn {

docs/site/src/theme/Footer/index.tsx

@@ -44,7 +44,7 @@ export default function Footer(): React.ReactElement {
         <div style={{display: 'flex', flexDirection: 'column', gap: '1rem'}}>
           <div style={{display: 'flex', alignItems: 'center', gap: '0.6rem'}}>
             <img src={logoUrl} alt="Erigon" style={{height: '32px', width: 'auto'}} />
-            <span style={{fontFamily: "'Montserrat', sans-serif", fontWeight: 800, fontSize: '1rem', letterSpacing: '0.04em'}}>erigon.tech</span>
+            <span style={{fontFamily: "'Quantify', sans-serif", fontWeight: 700, fontSize: '1rem', letterSpacing: '0.04em'}}>erigon.tech</span>
           </div>
           <p style={{
             fontSize: '0.875rem',