feat(portal): strip Vuexy demo content and create clean portal shell

Remove all demo pages, dialogs, sidebar navigation, and layout components.
Create minimal top-bar portal layout with auth-aware navigation, placeholder
pages for volunteer registration, dashboard, shifts, profile, artist advance,
and login. Add Pinia auth store, axios with Sanctum support, and router guards.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/portal/src/pages/[...path].vue

@@ -0,0 +1,36 @@
+<script setup lang="ts">
+definePage({
+  name: 'not-found',
+  meta: {
+    layout: 'blank',
+    requiresAuth: false,
+  },
+})
+</script>
+
+<template>
+  <VApp>
+    <VMain class="d-flex align-center justify-center" style="min-height: 100vh;">
+      <VCard
+        max-width="450"
+        width="100%"
+        class="text-center pa-6 ma-4"
+      >
+        <VCardTitle class="text-h4 mb-2">
+          404
+        </VCardTitle>
+        <VCardSubtitle class="text-h6 mb-4">
+          Pagina niet gevonden
+        </VCardSubtitle>
+        <VCardText>
+          <VBtn
+            color="primary"
+            to="/"
+          >
+            Terug naar home
+          </VBtn>
+        </VCardText>
+      </VCard>
+    </VMain>
+  </VApp>
+</template>