build: switch from yarn to npm to manage js dependencies and move js contents to root

yarn v1 is being deprecated and starts to have some issues

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

src/utils/validators.ts

@@ -0,0 +1,7 @@
+export function validateEmailField(value: string): boolean | string {
+  return value.includes("@") || "Invalid e-mail.";
+}
+
+export function validateRequiredField(value: unknown): boolean | string {
+  return !!value || "Required.";
+}