fix(prisma): provide fallback connection string when DATABASE_URL is unset during CI unit testing

memento-note/lib/prisma.ts

@@ -4,7 +4,7 @@ const prismaClientSingleton = () => {
   return new PrismaClient({
     datasources: {
       db: {
-        url: process.env.DATABASE_URL,
+        url: process.env.DATABASE_URL || 'postgresql://memento:memento@localhost:5432/memento',
       },
     },
   })