Add numbered pagination and redesign the IT/EN language switch

Blog and category archives now show a numbered page list (first, last,
current +/-1, collapsing gaps into an ellipsis) instead of only
previous/next — see shared/utils/pagination.ts's paginationRange().

Renders page links via NuxtLink's custom/v-slot API rather than letting
it render its own <a>: RouterLink's built-in active-class/aria-current
detection compares only the route's path, not its query string, so
every ?page=N link was incorrectly marked as the current page.

The language switch now shows both "Italiano / English" at all times,
with the current one as plain non-interactive text and the other as a
link, moved to the header's top-right corner instead of stacked under
the logo.

frontend/app/components/views/BlogIndexView.vue

@@ -47,21 +47,7 @@ useSeo({
         </li>
       </ul>
 
-      <nav v-if="data.pageCount > 1" class="pagination" :aria-label="strings.blog.paginationAriaLabel">
-        <NuxtLink v-if="data.page > 1" :to="{ query: { page: data.page - 1 } }" rel="prev">
-          {{ strings.blog.prevPage }}
-        </NuxtLink>
-        <span class="muted">
-          {{ interpolate(strings.blog.pageOf, { current: data.page, total: data.pageCount }) }}
-        </span>
-        <NuxtLink
-          v-if="data.page < data.pageCount"
-          :to="{ query: { page: data.page + 1 } }"
-          rel="next"
-        >
-          {{ strings.blog.nextPage }}
-        </NuxtLink>
-      </nav>
+      <PaginationNav :page="data.page" :page-count="data.pageCount" :locale="locale" />
     </template>
   </div>
 </template>