Switch to the package manager uv

[schneems]

We should update the app to use UV to match buildpack best practice recommendations

remote:  !     Note: We recently added support for the package manager uv:        
remote:  !     https://devcenter.heroku.com/changelog-items/3238        
remote:  !             
remote:  !     It's now our recommended Python package manager, since it        
remote:  !     supports lockfiles, is faster, gives more helpful error        
remote:  !     messages, and is actively maintained by a full-time team.        
remote:  !             
remote:  !     If you haven't tried it yet, we suggest you take a look!        

[edmorley]

@schneems Yeah this is already tracked in this GUS epic.