add: Zod validation schemas for form data and refactor server actions to use them

src/lib/server/validation.ts

@@ -90,3 +90,42 @@ export function sanitizeToken(token: string | null | undefined): string {
   }
   return trimmed;
 }
+
+// Zod schemas for type-safe form validation
+import { z } from 'zod';
+
+export const currencySchema = z.enum(['DKK', 'EUR', 'USD', 'SEK', 'NOK', 'GBP']);
+
+export const itemSchema = z.object({
+  title: z.string().min(1, 'Title is required').max(255),
+  description: z.string().max(2000).optional().nullable(),
+  link: z.string().url('Invalid URL').optional().nullable(),
+  imageUrl: z.string().url('Invalid image URL').optional().nullable(),
+  price: z.coerce.number().nonnegative().optional().nullable(),
+  currency: currencySchema.default('DKK'),
+  color: z.string().optional().nullable(),
+  order: z.coerce.number().int().nonnegative().optional()
+});
+
+export const updateItemSchema = itemSchema.extend({
+  id: z.string().min(1, 'Item ID is required')
+});
+
+export const wishlistSchema = z.object({
+  title: z.string().min(1, 'Title is required').max(255),
+  description: z.string().max(2000).optional().nullable(),
+  color: z.string().optional().nullable(),
+  theme: z.string().optional().nullable().transform((val) => val || 'none'),
+  endDate: z.coerce.date().optional().nullable()
+});
+
+export const reorderSchema = z.array(
+  z.object({
+    id: z.string(),
+    order: z.number().int().nonnegative()
+  })
+);
+
+export type ItemFormData = z.infer<typeof itemSchema>;
+export type UpdateItemFormData = z.infer<typeof updateItemSchema>;
+export type WishlistFormData = z.infer<typeof wishlistSchema>;