feat: create reusable UI components

- Add Header component with navigation and auth state
- Add Footer component with site information
- Add BIIcon component for Bootstrap Italia icons
- Add MemberDot component for member visualization
- Add default layout wrapper

Co-authored-by: Copilot <[email protected]>

app/layouts/default.vue

@@ -0,0 +1,28 @@
+<script setup lang="ts">
+import Header from "~/components/Header.vue";
+import Footer from "~/components/Footer.vue";
+</script>
+
+<template>
+  <div class="app-layout">
+    <Header />
+
+    <main class="app-main">
+      <slot />
+    </main>
+
+    <Footer />
+  </div>
+</template>
+
+<style scoped>
+.app-layout {
+  display: flex;
+  flex-direction: column;
+  min-height: 100vh;
+}
+
+.app-main {
+  flex-grow: 1;
+}
+</style>