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>

app/components/home/BookSection.vue

@@ -5,13 +5,12 @@
         <!-- Book cover -->
         <UiScrollReveal>
           <div class="book-cover-wrapper relative">
-            <div :class="['book-cover-3d', compact && 'book-cover-3d--compact']">
-              <img
-                :src="content?.book.coverImage"
-                :alt="content?.book.coverAlt"
-                class="book-cover-img"
-              />
-            </div>
+            <div
+              :class="['book-cover-3d', compact && 'book-cover-3d--compact']"
+              :style="{ backgroundImage: `url(${content?.book.coverImage})` }"
+              role="img"
+              :aria-label="content?.book.coverAlt"
+            />
           </div>
         </UiScrollReveal>
 
@@ -88,7 +87,12 @@ const titleLine2 = computed(() => titleParts.value[1])
 }
 
 .book-cover-3d {
+  width: 100%;
+  max-width: 360px;
   aspect-ratio: 3 / 4;
+  background-size: 200% auto;
+  background-position: right center;
+  background-repeat: no-repeat;
   border-radius: 0.75rem;
   overflow: hidden;
   border: 1px solid hsl(var(--color-text) / 0.1);
@@ -97,7 +101,6 @@ const titleLine2 = computed(() => titleParts.value[1])
     0 0 0 1px hsl(var(--color-text) / 0.08);
   transition: transform 0.5s cubic-bezier(0.645, 0.045, 0.355, 1),
               box-shadow 0.5s ease;
-  max-width: 360px;
 }
 
 .book-cover-3d--compact {
@@ -111,12 +114,6 @@ const titleLine2 = computed(() => titleParts.value[1])
     0 0 0 1px hsl(var(--color-primary) / 0.2);
 }
 
-.book-cover-img {
-  width: 200%;
-  height: 100%;
-  object-fit: cover;
-  transform: translateX(-50%);
-}
 
 .book-heading {
   font-size: clamp(1.625rem, 4vw, 2.125rem);