✨ Add layouts, routing, transitions & pages (Story 1.4)

Default layout with sticky AppHeader (nav, LanguageSwitcher, mobile hamburger),
AppFooter with social links. Minimal layout for express mode. 7 placeholder pages
with localized EN routes. Page transitions (fade+slide), prefers-reduced-motion
support, custom scroll behavior, error.vue, useSeo composable, SVG favicon.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/nuxt.config.ts

@@ -14,7 +14,7 @@ export default defineNuxtConfig({
     '@nuxtjs/sitemap',
   ],
 
-  css: ['~/assets/css/main.css'],
+  css: ['~/assets/css/main.css', '~/assets/css/transitions.css'],
 
   postcss: {
     plugins: {
@@ -33,6 +33,7 @@ export default defineNuxtConfig({
     lazy: true,
     langDir: '../i18n/',
     detectBrowserLanguage: false,
+    customRoutes: 'config',
     pages: {
       'projets/index': { en: '/projects' },
       'projets/[slug]': { en: '/projects/[slug]' },
@@ -46,13 +47,22 @@ export default defineNuxtConfig({
   },
 
   app: {
+    head: {
+      link: [
+        { rel: 'icon', type: 'image/svg+xml', href: '/favicon.svg' },
+      ],
+    },
     pageTransition: { name: 'page', mode: 'out-in' },
+    layoutTransition: { name: 'layout', mode: 'out-in' },
   },
 
   runtimeConfig: {
     public: {
       apiUrl: process.env.NUXT_PUBLIC_API_URL || 'http://localhost:8000/api',
       apiKey: process.env.NUXT_PUBLIC_API_KEY || '',
+      siteUrl: process.env.NUXT_PUBLIC_SITE_URL || 'https://skycel.fr',
+      githubUrl: process.env.NUXT_PUBLIC_GITHUB_URL || 'https://git.araneite.dev/skycel',
+      linkedinUrl: process.env.NUXT_PUBLIC_LINKEDIN_URL || '',
     },
   },