deprecate devenv-managed uv

[joshuarli]

devenv was created before uv existed and used to manage python versions, but now uv does that.

devenv manages per-repo uv installs but if people just installed uv globally via brew things would be even more simple:

• no need to bump uv (as needed to access future python versions) like here
• less devenv configuration
• global uv install = less setup needed per repo