feat: add VP_* to DEFAULT_UNTRACKED_ENV (#297)

## Summary

- Add `VP_*` pattern to `DEFAULT_UNTRACKED_ENV` so that Vite+ internal
environment variables (e.g. `VP_HOME`, `VP_VERSION`) are passed through
to child processes without affecting cache keys.

## Context

This is a prerequisite for
[voidzero-dev/vite-plus#1074](voidzero-dev/vite-plus#1074),
which renames all `VITE_PLUS_*` env vars to `VP_*` to avoid leaking
internal vars through Vite's `envPrefix` (default `VITE_`).

After the rename, `VP_*` vars no longer match the `VITE_*` fingerprinted
env pattern set by `vp build`. Without this change, `VP_VERSION` (and
other internal state vars) would be filtered out by
`EnvFingerprints::resolve()` and not reach child processes.

`VP_*` belongs in `untracked_env` (not `fingerprinted_envs`) because
these are internal runtime state variables that should not affect cache
keys.

Author: jong-kyung

crates/vite_task_graph/src/config/mod.rs

@@ -397,6 +397,8 @@ pub const DEFAULT_UNTRACKED_ENV: &[&str] = &[
     "COMPOSE_*",
     // Playwright specific
     "PLAYWRIGHT_*",
+    // Vite+ internal (not fingerprinted — internal state, not build-affecting)
+    "VP_*",
     // Token patterns
     "*_TOKEN",
 ];