feat: initial commit.

backend/sign-in.ts

@@ -0,0 +1,10 @@
+export async function backendSignIn(
+  email: string,
+  password: string,
+): Promise<boolean> {
+  // Simulate 1 second fetch
+  return new Promise((resolve) => {
+    const ok = email === "asdf@asdf" && password === "asdfasdf";
+    setTimeout(() => resolve(ok), 1000);
+  });
+}