add: GitHub authentication

src/app/(frontend)/login/page.tsx

@@ -0,0 +1,14 @@
+import { signIn } from "@/auth";
+
+export default function SignInButton() {
+  return (
+    <form
+      action={async () => {
+        "use server";
+        await signIn("github");
+      }}
+    >
+      <button type="submit">Sign In</button>
+    </form>
+  );
+}