feat(header): mobile hamburger menu + alignment & typography pass

- Header: offset the 4px green ::before bar so content centres in the
  visible dark area, not the geometric box (fixes wordmark/nav/icon
  sitting ~2px high — the root cause behind the whole alignment saga)
- Mobile (≤768px): collapse nav into a slide-down hamburger panel
  (standalone js/nav.js); inline nav retained on desktop
- Nav: use the display serif in sentence case so it shares the
  wordmark's anatomy and aligns naturally (no optical nudge needed)
- Typography tokens: three-tier display tracking (--tracking-display,
  --tracking-display-sm), --tracking-caps, --color-error, paper-glass
  overlays, --text-story/--leading-story; applied across components
- trip-dates: move inline styles to a class

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BftDn9vu9SonFAY4vxu4uk

themes/intotheeast/js/nav.js

@@ -0,0 +1,37 @@
+/* Mobile nav: hamburger toggle for the slide-down menu panel.
+   Standalone (not part of the esbuild bundle) — a small progressive
+   enhancement for the header. Loaded via base.html.twig. */
+(function () {
+    var toggle = document.querySelector('.nav-toggle');
+    var nav = document.getElementById('site-nav');
+    if (!toggle || !nav) return;
+
+    function setOpen(open) {
+        toggle.setAttribute('aria-expanded', open ? 'true' : 'false');
+        toggle.setAttribute('aria-label', open ? 'Close menu' : 'Open menu');
+        nav.setAttribute('data-open', open ? 'true' : 'false');
+    }
+
+    toggle.addEventListener('click', function (e) {
+        e.stopPropagation();
+        setOpen(toggle.getAttribute('aria-expanded') !== 'true');
+    });
+
+    /* Tapping a link closes the panel before navigating. */
+    nav.addEventListener('click', function (e) {
+        if (e.target.closest('a')) setOpen(false);
+    });
+
+    /* Close on outside tap or Escape. */
+    document.addEventListener('click', function (e) {
+        if (!nav.contains(e.target) && !toggle.contains(e.target)) setOpen(false);
+    });
+    document.addEventListener('keydown', function (e) {
+        if (e.key === 'Escape') setOpen(false);
+    });
+
+    /* Reset to closed if the viewport grows back to desktop. */
+    window.addEventListener('resize', function () {
+        if (window.innerWidth > 768) setOpen(false);
+    });
+})();