fix: handle stale tokens by checking user existence before creating walkthrough

backend/src/controllers/walkthrough.controller.ts

@@ -49,6 +49,15 @@ export const createWalkthrough = async (request: FastifyRequest, reply: FastifyR
         return reply.code(401).send({ message: 'Unauthorized' });
     }
 
+    // Verify user exists (handle stale tokens after re-seed)
+    const userExists = await request.server.prisma.user.findUnique({
+        where: { id: userId }
+    });
+
+    if (!userExists) {
+        return reply.code(401).send({ message: 'User not found. Please log in again.' });
+    }
+
     try {
         const walkthrough = await request.server.prisma.dailyWalkthrough.create({
             data: {
@@ -56,6 +65,7 @@ export const createWalkthrough = async (request: FastifyRequest, reply: FastifyR
                 completedBy: userId,
                 status: 'IN_PROGRESS',
             },
+
             include: {
                 user: {
                     select: {