✨ 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/app/router.options.ts

@@ -0,0 +1,27 @@
+import type { RouterConfig } from '@nuxt/schema'
+
+export default <RouterConfig>{
+  scrollBehavior(to, _from, savedPosition) {
+    if (savedPosition) {
+      return new Promise((resolve) => {
+        setTimeout(() => {
+          resolve(savedPosition)
+        }, 350)
+      })
+    }
+
+    if (to.hash) {
+      return {
+        el: to.hash,
+        behavior: 'smooth',
+        top: 80,
+      }
+    }
+
+    return new Promise((resolve) => {
+      setTimeout(() => {
+        resolve({ top: 0, behavior: 'smooth' })
+      }, 350)
+    })
+  },
+}