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.

tests/unit/LanguageSwitch.test.ts

@@ -0,0 +1,32 @@
+import { describe, expect, it } from 'vitest'
+import { mountSuspended, mockNuxtImport } from '@nuxt/test-utils/runtime'
+import { ref } from 'vue'
+import LanguageSwitch from '~/components/LanguageSwitch.vue'
+
+const langSwitchState = ref({ available: true, fallback: '/en/blog' })
+
+mockNuxtImport('useRoute', () => () => ({ path: '/blog/mio-slug' }))
+mockNuxtImport('useLocale', () => () => ref('it'))
+mockNuxtImport('useLangSwitchState', () => () => langSwitchState)
+
+describe('LanguageSwitch', () => {
+  it('shows the current language as non-interactive and the other as a link to /en', async () => {
+    langSwitchState.value = { available: true, fallback: '/en/blog' }
+
+    const wrapper = await mountSuspended(LanguageSwitch)
+
+    expect(wrapper.find('.lang-option.is-current').text()).toBe('Italiano')
+    expect(wrapper.find('.lang-option.is-current').attributes('aria-current')).toBe('true')
+
+    const link = wrapper.find('a.lang-option')
+    expect(link.text()).toBe('English')
+    expect(link.attributes('href')).toBe('/en/blog/mio-slug')
+  })
+
+  it('falls back to the given path when the current content has no translation', async () => {
+    langSwitchState.value = { available: false, fallback: '/en/blog' }
+
+    const wrapper = await mountSuspended(LanguageSwitch)
+    expect(wrapper.find('a.lang-option').attributes('href')).toBe('/en/blog')
+  })
+})