fix(build): speed up NSIS overlay install by async old dir removal

[winsan-zhang]

Replace synchronous RMDir /r with rename-then-async-delete strategy. The old install directory (3000+ files in cfmind/SKILLs/node_modules) was deleted synchronously in customInit, blocking the installer UI. Now we rename $INSTDIR instantly and delete in background via cmd /c. If rename fails, skip and let the installer's built-in uninstall handle it.

Summary

Related Issue

Fixes #(issue number)

Changes Made

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Code refactoring
• Documentation update
• Performance improvement
• Other (please describe):

Testing

• Tested locally
• Added new tests
• Updated existing tests
• Manual testing performed

Screenshots (if applicable)

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Electron-Specific Changes

• Changes to main process (src/main/)
• Changes to preload script (src/main/preload.ts)
• Changes to IPC communication
• Changes to window management
• None

Additional Notes