style(entropy-guide): rebuild on the dashboard's own sidebar + glass-card

Replaces the bespoke doc-page chrome with the app's real components:
DashboardSidebar shell (256px, rgba(0,0,0,.25) + 18px blur, staggered
nav-item entrance), the AnimatedLogo neode mark with its 20 staggered
squares, sidebar-nav-item + nav-tab-active for section state, and the
Settings wallpaper behind it all.

Every bespoke container (.card/.card-sm/.step/.score-card/.callout-*/
.diagram) is gone — .glass-card from style.css is now the only box on
the page, with layout-only grids inside it.

Scroll-spy lives in nav.js rather than inline, since the node's CSP is
script-src 'self'.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

neode-ui/public/entropy/nav.js

@@ -0,0 +1,29 @@
+// Scroll-spy for the sidebar, mirroring the dashboard's nav-tab-active state.
+// External file (not inline) because the node's CSP is script-src 'self'.
+(function () {
+  var links = Array.prototype.slice.call(
+    document.querySelectorAll('.sidebar-nav .sidebar-nav-item[href^="#"]')
+  )
+  if (!links.length || !('IntersectionObserver' in window)) return
+
+  var sections = links
+    .map(function (a) { return document.getElementById(a.getAttribute('href').slice(1)) })
+    .filter(Boolean)
+
+  function activate(id) {
+    links.forEach(function (a) {
+      a.classList.toggle('nav-tab-active', a.getAttribute('href') === '#' + id)
+    })
+  }
+
+  var visible = {}
+  var observer = new IntersectionObserver(function (entries) {
+    entries.forEach(function (e) { visible[e.target.id] = e.isIntersecting })
+    // Topmost section currently on screen wins, so the highlight tracks reading position.
+    for (var i = 0; i < sections.length; i++) {
+      if (visible[sections[i].id]) { activate(sections[i].id); return }
+    }
+  }, { rootMargin: '-10% 0px -70% 0px', threshold: 0 })
+
+  sections.forEach(function (s) { observer.observe(s) })
+})()