Feat: intégration multilingue FR/EN (i18n)

- Ajout de src/i18n/index.js : dictionnaire centralisé + fonction t(key, vars)
- Ajout de LanguageSwitcher.svelte : toggle FR/EN avec persistance localStorage
- Router : normalizePath strip /en/, apiPrefix() pour les fetches, détection langue (URL > localStorage > navigator)
- Tous les composants (Header, Menu, Footer, Article, Blog, Play) migrent vers t() depuis @i18n
- Blog : navigation interne (fetch, history, getSlugFromUrl) locale-aware

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/views/Blog.svelte

@@ -1,8 +1,10 @@
 <script>
   import { onMount } from 'svelte'
   import { slides } from '@state/slides.svelte'
+  import { locale } from '@state/locale.svelte'
   import Footer from '@components/layout/Footer.svelte'
   import Article from '@views/Article.svelte'
+  import { t } from '@i18n'
 
   let { data } = $props()
 
@@ -15,9 +17,9 @@
   let articleLoading = $state(false)
   let sectionEl = $state(null)
 
-  // Extract slug from current URL (for direct navigation to /blog/slug)
+  // Extract slug from current URL (for direct navigation to /blog/slug or /en/blog/slug)
   function getSlugFromUrl() {
-    const parts = window.location.pathname.split('/').filter(Boolean)
+    const parts = window.location.pathname.replace(/^\/en/, '').split('/').filter(Boolean)
     // parts = ['blog', 'slug'] → slug = 'slug'
     return parts.length >= 2 && parts[0] === 'blog' ? parts[1] : null
   }
@@ -25,7 +27,8 @@
   async function openArticle(slug) {
     articleLoading = true
     try {
-      const res = await fetch(`/blog/${slug}.json`)
+      const prefix = locale.current === 'en' ? '/en' : ''
+      const res = await fetch(`${prefix}/blog/${slug}.json`)
       if (!res.ok) throw new Error(`HTTP ${res.status}`)
       articleData = await res.json()
       scrollToTop()
@@ -39,7 +42,8 @@
 
   function backToList() {
     articleData = null
-    history.pushState({}, '', '/blog')
+    const prefix = locale.current === 'en' ? '/en' : ''
+    history.pushState({}, '', `${prefix}/blog`)
     document.title = `${data?.title ?? 'Blog'} — World Game`
     scrollToTop()
   }
@@ -56,12 +60,13 @@
     const url = new URL(link.href, window.location.origin)
     if (url.origin !== window.location.origin) return
 
-    const match = url.pathname.match(/^\/blog\/([^/]+)$/)
+    const match = url.pathname.match(/^(?:\/en)?\/blog\/([^/]+)$/)
     if (match) {
       e.preventDefault()
       e.stopPropagation()
       const slug = match[1]
-      history.pushState({}, '', `/blog/${slug}`)
+      const prefix = locale.current === 'en' ? '/en' : ''
+      history.pushState({}, '', `${prefix}/blog/${slug}`)
       openArticle(slug)
     }
   }
@@ -129,7 +134,7 @@
               <p class="blog-card-description">{featured.intro}</p>
             {/if}
             <a href="/blog/{featured.slug}" class="blog-card-readmore">
-              Lire l'article <span class="arrow">→</span>
+              {t('read_article')} <span class="arrow">→</span>
             </a>
           </div>
           {#if featured.cover}
@@ -151,7 +156,7 @@
               <a href="/blog/{article.slug}">{article.title}</a>
             </h2>
             <a href="/blog/{article.slug}" class="blog-card-readmore">
-              Lire l'article <span class="arrow">→</span>
+              {t('read_article')} <span class="arrow">→</span>
             </a>
           </div>
           {#if article.cover}
@@ -168,7 +173,7 @@
       {/each}
 
       {#if articleLoading}
-        <p class="blog-loading">Chargement…</p>
+        <p class="blog-loading">{t('loading')}</p>
       {/if}
 
     </div>