feat(cli): add --dry-run to init to preview install actions without writing (#489)
Closes#291
- Adds resolveInstallPaths helper shared by real install and dry-run preview
- New planPlatformInstallActions / planAllPlatformInstallActions for read-only preview
- 3 e2e tests verify output content, no-write guarantee, and all-platforms coverage
- README docs included
*Approved and merged by github-maintain cron*
