feat(portal): migrate option consumers to relational rich shape

Aligns the portal form renderer with the post-WS-5d snapshot + resource
contract. FieldRadio, FieldSelect, FieldMultiselect, and FieldCheckboxList
now consume options as arrays of {value, label, sort_order, translations?}
objects instead of the legacy string | {label, description, value?} union.

Locale resolution: option-level translations[locale] is preferred over
the default label when the active form locale is non-default. Pages
provide the locale via providePublicFormLocale (new helper in
publicFormInjection, mirrors providePublicFormToken). Field components
inject via usePublicFormLocale, which falls back to 'nl' when no
provider is on the tree — keeps standalone component tests light.
[public_token].vue now provides schemaQuery.data.locale ?? 'nl' to all
option-bearing renderers.

TypeScript types updated: PublicFormField.options is now OptionSpec[] |
null in @form-schema/types/formBuilder. The legacy `FieldOption` union
type is gone — passing strings or {label, description} would now fail
type-check. resolveOptionLabel(option, locale) helper exported from the
same module is the single source of truth for label resolution.

The legacy per-option `description` field is dropped as part of the
type narrowing — ARCH §5.1's option-bearing field types
(RADIO/SELECT/MULTISELECT/CHECKBOX_LIST) don't model descriptions; the
parallel RegistrationFieldTemplate domain in apps/app keeps its own
description support which is orthogonal and out of WS-5d scope. The 4
migrated components no longer render the description subtitle/paragraph
(both Vuetify item slots and the radio/checkbox custom #label slots
removed).

apps/app is NOT touched in this commit — its only options-reading
components (RegistrationField*.vue) consume the legacy
registration_field_templates / registration_form_fields domain and are
out of WS-5d scope. The commit-3 secondary filter-registry scan
returned zero portal+app consumers as predicted, so commit 4 stays
portal-only.

Vitest: 102 → 111 passed (+9 new tests in FieldOptionsLocale.spec.ts
covering preference of translations[locale] over label, fallback on
missing translation, and default-locale-no-provider fall-through, for
each of the four migrated components plus a no-provider sanity test).
The 2 pre-existing failures in FieldSectionPriority.spec.ts (stale
post-WS-5b max_priorities → max_selected references) are out of WS-5d
scope; the failure baseline is unchanged.

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

apps/portal/src/pages/register/[public_token].vue

@@ -11,7 +11,7 @@ import { usePublicFormTimeSlots } from '@/composables/api/usePublicFormTimeSlots
 import { useFormDraft } from '@/composables/useFormDraft'
 import { isStepValid, useFormSteps } from '@form-schema/composables/useFormSteps'
 import { formatFieldValue } from '@form-schema/composables/formatFieldValue'
-import { providePublicFormToken } from '@/composables/publicFormInjection'
+import { providePublicFormLocale, providePublicFormToken } from '@/composables/publicFormInjection'
 import { FormFieldType } from '@form-schema/types/formBuilder'
 import type { FormErrorCode, PublicFormField } from '@form-schema/types/formBuilder'
 
@@ -40,6 +40,13 @@ providePublicFormToken(token)
 
 const schemaQuery = useFetchPublicFormSchema(tokenRef)
 
+// Surface the schema's locale to option-bearing field renderers so they
+// can resolve per-option translations[locale] over the default label.
+// Defaults to 'nl' until the schema resolves.
+const formLocale = computed<string>(() => schemaQuery.data.value?.locale ?? 'nl')
+
+providePublicFormLocale(formLocale)
+
 // Sibling endpoints — fetched at page level so the review step and
 // FormConfirmation can human-label AVAILABILITY_PICKER /
 // SECTION_PRIORITY values via formatFieldValue. Shares the same