* feat(uv-env): create plugin
This plugin automatically activates/deactivates a uv-managed virtual
environment when you cd into or out of a project directory. It looks
for pyproject.toml and uv.lock to detect a uv project, and reads
UV_PROJECT_ENVIRONMENT to support custom venv locations.
* fix(uv-env): address review feedback from robbyrussell
- Add `local` to venv_dir to prevent leaking into user's shell
- Replace `export` with `typeset -g` for uv_active and uv_dir
- Use `autoload -Uz` to match the style guide
