Detect Codex installs managed by Vite+

[charliemarsh-oai]

Summary

• detect Vite+ global installations from their package layout before falling back to npm metadata
• propagate a dedicated Vite+ install method through doctor and update surfaces
• use vp install -g @openai/codex when repairing or updating Vite+-managed installs

Why

Vite+ installs @openai/codex under VP_HOME/packages but launches through the same JavaScript shim as npm. The shim previously treated any non-Bun launch as npm-managed, so doctor and update flows suggested npm even though Vite+ owned the package. A dedicated marker keeps ownership accurate and clears stale package-manager markers before launching the native binary.

Focused install-context and update-action coverage passes, including a smoke test using the Vite+ directory layout. Scoped Clippy, formatting, and diff checks pass. The broader affected-crate run passed 3,260 tests; two unrelated Guardian tests failed identically on main.

Closes #30698.