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/components/BIIcon.vue

@@ -0,0 +1,20 @@
+<script setup lang="ts">
+defineProps<{
+  name: string
+  size?: 'xs' | 'sm' | 'lg' | 'xl'
+  color?: 'primary' | 'success' | 'warning' | 'danger' | 'info' | 'white'
+}>()
+</script>
+
+<template>
+  <svg
+      class="icon"
+      :class="[
+      size ? `icon-${size}` : '',
+      color ? `icon-${color}` : ''
+    ]"
+      aria-hidden="true"
+  >
+    <use :href="`/sprites.svg#${name}`"></use>
+  </svg>
+</template>