Added AI skills

.agents/skills/react-hook-form/references/integ-value-transform.md

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+---
+title: Transform Values at Controller Level for Type Coercion
+impact: MEDIUM
+impactDescription: stops string input values reaching a number- or date-typed schema
+tags: integ, transform, value-coercion, Controller
+---
+
+## Transform Values at Controller Level for Type Coercion
+
+Native inputs return strings. When your form needs numbers, dates, or other types, transform values in the Controller render function rather than relying solely on `valueAsNumber` or `valueAsDate`.
+
+**Incorrect (valueAsNumber has edge cases):**
+
+```typescript
+function QuantityInput() {
+  const { register } = useForm()
+
+  return (
+    <input
+      {...register('quantity', { valueAsNumber: true })}  // Returns NaN for empty string
+      type="number"
+    />
+  )
+}
+```
+
+**Correct (explicit transformation in Controller):**
+
+```typescript
+function QuantityInput({ control }: { control: Control }) {
+  return (
+    <Controller
+      name="quantity"
+      control={control}
+      render={({ field }) => (
+        <input
+          type="number"
+          value={field.value ?? ''}
+          onChange={(e) => {
+            const value = e.target.value
+            field.onChange(value === '' ? null : parseInt(value, 10))
+          }}
+          onBlur={field.onBlur}
+        />
+      )}
+    />
+  )
+}
+```
+
+**Alternative (Zod transform at schema level):**
+
+```typescript
+const schema = z.object({
+  quantity: z.string().transform((val) => (val === '' ? null : parseInt(val, 10))),
+})
+```
+
+Reference: [React Hook Form - Advanced Usage](https://react-hook-form.com/advanced-usage)