sign in and register fixes for looped and forwarded pages

lib/jwt.ts

@@ -0,0 +1,15 @@
+// lib/jwt.ts
+export function jwtExp(token?: string | null): number | null {
+    if (!token) return null;
+    try {
+        const payload = JSON.parse(Buffer.from(token.split(".")[1], "base64").toString("utf8"));
+        return typeof payload?.exp === "number" ? payload.exp : null;
+    } catch {
+        return null;
+    }
+}
+
+export function isJwtValid(token?: string | null): boolean {
+    const exp = jwtExp(token);
+    return !!exp && exp * 1000 > Date.now();
+}