refactor(form-schema): extract schema types and schema-driven behaviors to shared package

Moves formBuilder types, formValidation, useConditionalLogic, useFormSteps,
and formatFieldValue from apps/portal/src to packages/form-schema/src.
Adds @form-schema path alias to both apps/portal and apps/app.
Vue field components remain per-app to allow independent visual evolution.
Behavior-neutral: all 35 Vitest tests green.

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

apps/portal/src/components/public-form/FieldParagraph.vue

@@ -1,5 +1,5 @@
 <script setup lang="ts">
-import type { PublicFormField } from '@/types/formBuilder'
+import type { PublicFormField } from '@form-schema/types/formBuilder'
 
 defineProps<{
   field: PublicFormField