refactor(portal): move pages from apps/portal to apps/app

Per WS-3 PR-B1 charter §4.2: portal pages relocate into the
single-SPA layout under apps/app/src/pages/portal/** (authenticated
portal context) and apps/app/src/pages/register/** (public
token-based form-fill / confirmation).

Updated meta blocks:
  - Portal pages: layout: 'PortalLayout', context: 'portal'
    (preserving original requiresAuth + nav fields)
  - Register pages: layout: 'PublicLayout' (drop requiresAuth)

Skipped (apps/portal duplicates of pages already in apps/app):
  index.vue, login.vue, wachtwoord-{vergeten,resetten}.vue,
  verify-email-change.vue. Deleted: [...path].vue (apps/app already
  has [...error].vue catch-all).

NOTE: Component/store/composable imports inside these files still
point at apps/portal-relative paths and will be rewritten in the
next commits. Build will not be green again until commit 6
(composables/lib).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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

@@ -1,36 +0,0 @@
-<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>