✨ 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/layouts/default.vue

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+<template>
+  <div class="min-h-screen bg-sky-dark text-sky-text flex flex-col">
+    <LayoutAppHeader />
+
+    <main class="flex-1">
+      <slot />
+    </main>
+
+    <LayoutAppFooter />
+  </div>
+</template>

frontend/app/layouts/minimal.vue

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+<template>
+  <div class="min-h-screen bg-sky-dark text-sky-text flex flex-col">
+    <header class="p-4 flex justify-between items-center">
+      <NuxtLink :to="localePath('/')" class="text-sky-accent font-narrative font-bold">
+        Skycel
+      </NuxtLink>
+      <div class="flex items-center gap-4">
+        <NuxtLink :to="localePath('/')" class="text-sky-text/70 hover:text-sky-accent text-sm font-ui transition-colors">
+          {{ $t('common.back_to_adventure') }}
+        </NuxtLink>
+        <UiLanguageSwitcher />
+      </div>
+    </header>
+
+    <main class="flex-1">
+      <slot />
+    </main>
+
+    <footer class="p-4 text-center text-sky-text/50 text-sm font-ui">
+      {{ $t('footer.copyright', { year: new Date().getFullYear() }) }}
+    </footer>
+  </div>
+</template>
+
+<script setup lang="ts">
+const localePath = useLocalePath()
+</script>