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>

packages/form-schema/README.md

@@ -0,0 +1,19 @@
+# @form-schema
+
+Shared schema contract and schema-driven behaviors for Crewli form rendering. Consumed by apps/portal (public submission) and apps/app (organizer builder + submissions review).
+
+## What lives here
+
+- `types/` — TypeScript types and enum constants mirroring backend `FormBuilder` enums and `PublicForm(Schema|Submission)Resource`
+- `utils/formValidation.ts` — validation rule builders driven by `FormFieldValidationRules`
+- `composables/useConditionalLogic.ts` — evaluate `conditional_logic.show_when` against field values
+- `composables/useFormSteps.ts` — step navigation logic for multi-step forms
+- `composables/formatFieldValue.ts` — render a stored submission value as a human-readable string
+
+## What does NOT live here
+
+Vue components. Each app renders its own UI. Portal has full-fidelity submit components; app has builder-preview and submissions-review components. Sharing renderers would couple the two apps' visual styles, which we explicitly want to avoid.
+
+## Contract stability
+
+This is an alias-only shared directory inside the monorepo — no npm package, no semver. Breaking changes (new field type, new validation key, new conditional operator) require updating both apps in the same PR. TypeScript will flag missing cases in dispatchers.