Load .env environment variables for `vite dev`

[ryansch]

Description 📖

This pull request ensures that Rails has initialized before running the vite dev server.

Background 📜

I noticed that setting VITE_RUBY_* environment variables via .env.* files would work for vite build but not for vite dev.

The Fix 🔨

I generalized the ViteRails::CLI::Build module to apply to both vite build and vite dev.