fix: cache only the version-specific directory, not entire ~/.vite-plus

Previously cached the whole ~/.vite-plus/ directory, which could include
Node.js state from `vp env use` and mutations from later workflow steps.
Now caches only ~/.vite-plus/{version}/ and recreates the current/bin
symlinks after restore. This prevents cross-contamination in multi-Node
matrix builds and avoids baking unrelated state into the cache.

Author: fengmk2