security: A01-13 — nest all event routes under organisation prefix

Move all authenticated organiser-facing event sub-resource routes from
/events/{event}/... to /organisations/{organisation}/events/{event}/...
to enforce multi-tenancy at the routing layer.

Changes:
- Routes: restructured api.php to nest all event sub-resources under
  the existing organisation prefix group
- Controllers: added Organisation parameter and VerifiesOrganisationEvent
  trait to all 12 affected controllers (sections, time-slots, shifts,
  persons, crowd-lists, locations, shift-assignments, registration-fields,
  availabilities, field-values, section-preferences, stats)
- Tests: updated all 20 feature test files with new route paths
- Frontend: updated 8 API composables and 20 Vue components/pages
- API.md: updated documentation to reflect new route structure

Portal routes, public routes (volunteer-register), and invitation routes
remain unchanged as they operate without organisation context.

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

apps/app/src/components/sections/EditSectionDialog.vue

@@ -35,7 +35,7 @@ const form = ref({
 const errors = ref<Record<string, string>>({})
 const refVForm = ref<VForm>()
 
-const { mutate: updateSection, isPending } = useUpdateSection(eventIdRef)
+const { mutate: updateSection, isPending } = useUpdateSection(orgId, eventIdRef)
 
 const typeOptions = [
   { title: 'Standaard', value: 'standard' },