fix: corrections lecteur PDF + couverture + navigation chapitres

- PDF viewer : suppression animation/lock isAnimating, navigation stable
- PDF reader : focus iframe au chargement → flèches actives immédiatement
- BookSection : couverture via background-image (right center) — fiable
- AxisBlock : boutons secondaires NuxtLink/button explicites (v-if/v-else)
- modele-eco/[slug] : scroll top au changement de chapitre (SPA reuse)
- router.options.ts : scrollBehavior global top/instant
- PDF mis à jour (numéros de pages chapitres 7–11)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

public/pdfjs/viewer.html

@@ -158,24 +158,6 @@ html, body {
   visibility: hidden;
 }
 
-/* Page turn transition */
-.page-slot canvas {
-  transition: opacity 1s ease-out, transform 1s ease-out;
-}
-
-.page-slot canvas.entering {
-  opacity: 0;
-  transform: translateX(var(--enter-dir, 20px));
-  transition: none;
-}
-
-.page-slot canvas.leaving {
-  opacity: 0;
-  transform: translateX(var(--leave-dir, -20px));
-  position: absolute;
-  transition: opacity 1.2s ease-in, transform 1.2s ease-in;
-}
-
 /* Navigation bar */
 .nav-bar {
   display: flex;
@@ -300,8 +282,6 @@ let currentSpread = 0; // index into spreads[]
 let spreads = [];       // [[1], [2,3], [4,5], ...] — page 1 alone (cover), then pairs
 let pageCanvasCache = new Map();
 let outlinePageMap = []; // [{item, pageNum}] for highlighting
-let isAnimating = false;
-
 function buildSpreads(numPages) {
   spreads = [];
   // Page 1 = couverture seule
@@ -347,33 +327,14 @@ async function renderPageCanvas(pageNum) {
   return canvas;
 }
 
-async function showSpread(index, animate = true) {
+async function showSpread(index) {
   if (index < 0 || index >= spreads.length) return;
-  if (isAnimating) return;
 
-  const prevIndex = currentSpread;
-  const direction = index > prevIndex ? 1 : -1; // 1 = forward, -1 = back
   currentSpread = index;
-
   const pages = spreads[index];
   const slotLeft = document.getElementById('slotLeft');
   const slotRight = document.getElementById('slotRight');
 
-  // Collect old canvases for fade-out
-  const oldCanvases = [...slotLeft.querySelectorAll('canvas'), ...slotRight.querySelectorAll('canvas')];
-  const shouldAnimate = animate && oldCanvases.length > 0;
-
-  if (shouldAnimate) {
-    isAnimating = true;
-    // Fade out old canvases with directional slide
-    oldCanvases.forEach(c => {
-      c.style.setProperty('--leave-dir', `${-direction * 20}px`);
-      c.classList.add('leaving');
-    });
-    // Wait for fade-out to mostly complete
-    await new Promise(r => setTimeout(r, 500));
-  }
-
   slotLeft.innerHTML = '';
   slotRight.innerHTML = '';
   slotLeft.className = 'page-slot';
@@ -381,40 +342,17 @@ async function showSpread(index, animate = true) {
 
   if (pages.length === 1) {
     const canvas = await renderPageCanvas(pages[0]);
-    if (shouldAnimate) {
-      canvas.style.setProperty('--enter-dir', `${direction * 20}px`);
-      canvas.classList.add('entering');
-    }
     slotLeft.appendChild(canvas);
     slotRight.className = 'page-slot empty';
-    if (shouldAnimate) {
-      // Double rAF ensures the browser has painted the initial state before transitioning
-      requestAnimationFrame(() => requestAnimationFrame(() => canvas.classList.remove('entering')));
-    }
   } else {
     const [left, right] = await Promise.all([
       renderPageCanvas(pages[0]),
       renderPageCanvas(pages[1]),
     ]);
-    if (shouldAnimate) {
-      left.style.setProperty('--enter-dir', `${direction * 20}px`);
-      right.style.setProperty('--enter-dir', `${direction * 20}px`);
-      left.classList.add('entering');
-      right.classList.add('entering');
-    }
     slotLeft.appendChild(left);
     slotRight.appendChild(right);
-    if (shouldAnimate) {
-      requestAnimationFrame(() => requestAnimationFrame(() => {
-        left.classList.remove('entering');
-        right.classList.remove('entering');
-      }));
-    }
   }
 
-  if (shouldAnimate) setTimeout(() => { isAnimating = false; }, 1100);
-  else isAnimating = false;
-
   updateNav();
   highlightOutline();
 }