feat: add form field validators

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/utils/validators.ts

@@ -0,0 +1,48 @@
+import { FormField } from '../types';
+
+export interface ValidationError {
+  fieldId: string;
+  message: string;
+}
+
+/**
+ * Validate form values against field definitions.
+ * Returns an empty array if everything is valid.
+ */
+export function validateForm(
+  fields: FormField[],
+  values: Record<string, unknown>,
+): ValidationError[] {
+  const errors: ValidationError[] = [];
+
+  for (const field of fields) {
+    const value = values[field.id];
+
+    if (field.required) {
+      if (value === undefined || value === null || value === '') {
+        errors.push({ fieldId: field.id, message: `${field.label} is required.` });
+        continue;
+      }
+      if (Array.isArray(value) && value.length === 0) {
+        errors.push({ fieldId: field.id, message: `${field.label} is required.` });
+        continue;
+      }
+    }
+
+    if (value !== undefined && value !== null && value !== '') {
+      if (field.type === 'number' && typeof value === 'string') {
+        if (isNaN(Number(value))) {
+          errors.push({ fieldId: field.id, message: `${field.label} must be a number.` });
+        }
+      }
+      if (field.type === 'rating') {
+        const n = Number(value);
+        if (isNaN(n) || n < 1 || n > 5) {
+          errors.push({ fieldId: field.id, message: `${field.label} must be between 1 and 5.` });
+        }
+      }
+    }
+  }
+
+  return errors;
+}