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/book/BookPdfReader.vue

@@ -1,13 +1,12 @@
 <template>
   <Teleport to="body">
-    <Transition name="pdf-overlay">
-      <div
-        v-if="isOpen"
-        class="pdf-reader"
-        @keydown.escape="close"
-        tabindex="0"
-        ref="overlayRef"
-      >
+    <div
+      v-if="isOpen"
+      class="pdf-reader"
+      @keydown.escape="close"
+      tabindex="0"
+      ref="overlayRef"
+    >
         <!-- Top bar -->
         <div class="pdf-bar">
           <div class="pdf-bar-title">
@@ -26,10 +25,11 @@
             :src="pdfUrl"
             class="pdf-frame"
             :title="bpContent?.pdf.iframeTitle"
+            ref="iframeRef"
+            @load="iframeRef?.focus()"
           />
         </div>
-      </div>
-    </Transition>
+    </div>
   </Teleport>
 </template>
 
@@ -42,6 +42,7 @@ const bookData = useBookData()
 await bookData.init()
 
 const overlayRef = ref<HTMLElement>()
+const iframeRef = ref<HTMLIFrameElement>()
 
 const isOpen = computed({
   get: () => props.modelValue,
@@ -138,15 +139,4 @@ onUnmounted(() => {
   background: white;
 }
 
-/* Overlay transitions */
-.pdf-overlay-enter-active {
-  animation: pdf-enter 0.4s cubic-bezier(0.16, 1, 0.3, 1) both;
-}
-.pdf-overlay-leave-active {
-  animation: pdf-enter 0.3s cubic-bezier(0.7, 0, 0.84, 0) reverse both;
-}
-@keyframes pdf-enter {
-  from { opacity: 0; transform: translateY(8px); }
-  to { opacity: 1; transform: translateY(0); }
-}
 </style>