docs: use ~/.vfox as the user directory in uninstall and config guides

[azzliang6]

The uninstall guide tells users to run rm -rf ~/.version-fox, but since 1.0.0 vfox uses ~/.vfox. It only falls back to ~/.version-fox when that legacy directory already exists (see NewPathMeta in internal/pathmeta/path_meta.go).

Changes, in both the English and Chinese docs:

• uninstallation: use rm -rf ~/.vfox and add a short note about the pre-1.0.0 ~/.version-fox directory
• configuration: replace $HOME/.version-fox with $HOME/.vfox for config.yaml and the cache dir, and fix the available-hook cache path to $HOME/.vfox/plugin/<plugin-name>/.available.cache, which is where sdk.Available actually writes it

multi-user-sharing.md already describes the old and new names correctly, so I left it alone.

Closes #711

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 35.09%. Comparing base (930f5be) to head (40e779b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #714   +/-   ##
=======================================
  Coverage   35.09%   35.09%           
=======================================
  Files          92       92           
  Lines        6514     6514           
=======================================
  Hits         2286     2286           
  Misses       3922     3922           
  Partials      306      306           

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[aooohan]

Thanks for the first contribution.