I think that the comments are confusing work for hire in the context of being an employee v. a contract worker. Your contract seems to say that if you do subcontract work it will be considered produced for the company (see Cmty. for Creative Non-Violence v. Reid, 490 U.S. 730). The question in re your case is whether the app falls within your scope of employment. If you really think it is worth something, you should talk to a copyright attorney.