Fix slide snap + presentation keyboard nav

- html/body height 100%, html overflow-y scroll — proper snap container
- box-sizing border-box on sections (padding wasn't being included)
- 2px black border-top between slides — visual divider
- frame display block, body margin 0
- Keyboard: ArrowDown/PageDown/Space → next, ArrowUp/PageUp → prev,
  Home/End → first/last

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

index.html

@@ -106,13 +106,18 @@
   }
 }
 
+html, body {
+  height: 100%;
+}
 html {
   scroll-behavior: smooth;
-  font-size: clamp(18px, 1.6vw, 28px); /* масштабируется под экран — для проектора 24–28px */
+  font-size: clamp(18px, 1.6vw, 28px);
   scroll-snap-type: y mandatory;
+  overflow-y: scroll;
+  scroll-padding-top: 0;
 }
 
-/* PRESENTATION MODE: каждая секция = ровно 1 экран, фиксация при скролле */
+/* PRESENTATION MODE: каждая секция = ровно 1 экран */
 .hero,
 section.section,
 .dark-section {
@@ -124,7 +129,7 @@ section.section,
   justify-content: center;
   padding-top: 4vh;
   padding-bottom: 4vh;
-  overflow-y: auto; /* если контент длиннее — скролл внутри слайда */
+  box-sizing: border-box;
 }
 
 /* Усиливаем типографику для большого экрана */
@@ -184,9 +189,18 @@ body {
   font-family: 'Lora', Georgia, serif !important;
   background: var(--page-bg);
   padding: 0;
+  margin: 0;
+  overflow: visible;
 }
 
-.frame { gap: 0; min-height: 100dvh; }
+.frame { gap: 0; min-height: 100dvh; display: block; }
+
+/* Усиливаем визуальную границу между слайдами */
+.hero, section.section, .dark-section {
+  border-top: 2px solid var(--text) !important;
+  position: relative;
+}
+.hero { border-top: none !important; }
 
 /* Шрифты заголовков */
 .hero-title, .section-title, .dark-title,
@@ -3061,16 +3075,18 @@ const SCHEDULE = [
       targets.forEach(el => io.observe(el));
     })();
 
-    // Slide counter — показывает текущий слайд / всего
+    // Slide counter + keyboard nav (PageDown / Arrow / Space)
     (function() {
       const counter = document.getElementById('slide-counter');
-      if (!counter) return;
       const slides = Array.from(document.querySelectorAll('.hero, section.section, .dark-section'));
       const total = slides.length;
+      let current = 0;
       const update = (idx) => {
-        counter.textContent = `— ${idx + 1} / ${total} —`;
+        current = idx;
+        if (counter) counter.textContent = `— ${idx + 1} / ${total} —`;
       };
       update(0);
+
       const io = new IntersectionObserver((entries) => {
         entries.forEach(e => {
           if (e.isIntersecting && e.intersectionRatio > 0.5) {
@@ -3080,6 +3096,24 @@ const SCHEDULE = [
         });
       }, { threshold: [0.5, 0.6, 0.75] });
       slides.forEach(s => io.observe(s));
+
+      const goTo = (idx) => {
+        idx = Math.max(0, Math.min(total - 1, idx));
+        slides[idx].scrollIntoView({ behavior: 'smooth', block: 'start' });
+      };
+
+      document.addEventListener('keydown', (e) => {
+        if (['INPUT', 'TEXTAREA'].includes(document.activeElement?.tagName)) return;
+        if (e.key === 'ArrowDown' || e.key === 'PageDown' || e.key === ' ') {
+          e.preventDefault(); goTo(current + 1);
+        } else if (e.key === 'ArrowUp' || e.key === 'PageUp') {
+          e.preventDefault(); goTo(current - 1);
+        } else if (e.key === 'Home') {
+          e.preventDefault(); goTo(0);
+        } else if (e.key === 'End') {
+          e.preventDefault(); goTo(total - 1);
+        }
+      });
     })();
   </script>
 </body>