feat(portal): multi-step volunteer registration form with public event endpoint

- Add GET /api/v1/public/events/{slug}/registration-data endpoint for fetching
  event sections and time slots without auth
- Create 5-step registration form: personal info, details, motivation, section
  preferences, availability
- VeeValidate + Zod validation per step with Dutch error messages
- Auth-aware: pre-fills name/email for authenticated users
- Mobile responsive with custom chip-based step indicator
- Success page with contextual actions (dashboard vs login)
- Types, composable (TanStack Query), and Zod schemas

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

apps/portal/src/schemas/registrationSchema.ts

@@ -0,0 +1,24 @@
+import { z } from 'zod'
+
+export const step1Schema = z.object({
+  name: z.string().min(1, 'Naam is verplicht').max(255),
+  email: z.string().min(1, 'E-mailadres is verplicht').email('Ongeldig e-mailadres').max(255),
+  phone: z.string().max(50).optional().or(z.literal('')),
+})
+
+export const step2Schema = z.object({
+  tshirt_size: z.enum(['XS', 'S', 'M', 'L', 'XL', 'XXL', 'XXXL']).optional().or(z.literal('')),
+  first_aid: z.boolean().default(false),
+  allergies: z.string().max(500).optional().or(z.literal('')),
+  access_requirements: z.string().max(500).optional().or(z.literal('')),
+  driving_licence: z.boolean().default(false),
+})
+
+export const step3Schema = z.object({
+  motivation: z.string().max(1000).optional().or(z.literal('')),
+  motivation_other: z.string().max(500).optional().or(z.literal('')),
+})
+
+export const fullRegistrationSchema = step1Schema
+  .merge(step2Schema)
+  .merge(step3Schema)