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/AxisBlock.vue

@@ -72,17 +72,25 @@
           </div>
           <!-- Secondary row -->
           <div v-if="secondaryActions(item.actions).length" class="axis-actions-secondary">
-            <component
-              :is="action.to ? resolveComponent('NuxtLink') : 'button'"
-              v-for="action in secondaryActions(item.actions)"
-              :key="action.label"
-              :to="action.to"
-              class="axis-action-btn axis-action-btn--secondary"
-              @click.stop="!action.to && handleAction(action.id)"
-            >
-              <div :class="iconClass(action.icon)" class="h-3.5 w-3.5" />
-              {{ action.label }}
-            </component>
+            <template v-for="action in secondaryActions(item.actions)" :key="action.label">
+              <NuxtLink
+                v-if="action.to"
+                :to="action.to"
+                class="axis-action-btn axis-action-btn--secondary"
+                @click.stop
+              >
+                <div :class="iconClass(action.icon)" class="h-3.5 w-3.5" />
+                {{ action.label }}
+              </NuxtLink>
+              <button
+                v-else
+                class="axis-action-btn axis-action-btn--secondary"
+                @click.stop="handleAction(action.id)"
+              >
+                <div :class="iconClass(action.icon)" class="h-3.5 w-3.5" />
+                {{ action.label }}
+              </button>
+            </template>
           </div>
         </div>
       </div>