feat(validation): add arktype form schemas and i18n keys

Introduces field-specific validation messages so toasts name the
exact field and rule that failed instead of a catch-all "tous les
champs sont requis".

src/schemas/transaction.ts

@@ -0,0 +1,24 @@
+import { type } from 'arktype'
+
+export const MAX_TRANSACTION_AMOUNT = 1_000_000
+
+export const transactionFormSchema = type({
+  name: 'unknown',
+  amount: 'unknown',
+  payBy: 'unknown'
+}).narrow((data, ctx) => {
+  if (typeof data.name !== 'string' || data.name.trim().length === 0) {
+    ctx.reject({ message: 'validation.transaction_name_required', path: ['name'] })
+  }
+  if (typeof data.amount !== 'number' || Number.isNaN(data.amount)) {
+    ctx.reject({ message: 'validation.amount_required', path: ['amount'] })
+  } else if (data.amount <= 0) {
+    ctx.reject({ message: 'validation.amount_must_be_positive', path: ['amount'] })
+  } else if (data.amount > MAX_TRANSACTION_AMOUNT) {
+    ctx.reject({ message: 'validation.amount_too_large', path: ['amount'] })
+  }
+  if (typeof data.payBy !== 'string' || data.payBy.length === 0) {
+    ctx.reject({ message: 'validation.pay_by_required', path: ['payBy'] })
+  }
+  return !ctx.hasError()
+})