- Update system attribute to stdenv.hostPlatform.system in overlays
- Migrate git config to new settings structure (user.name, user.email)
- Move ssh.addKeysToAgent to matchBlocks configuration
- Disable ssh default config to prevent future deprecation warnings
Configure nix.gc to automatically clean up old home-manager generations
weekly, which complements the existing system-level gc. Uses
--delete-older-than 10d on Linux to maintain a rollback window, but
overrides to -d on Darwin to work around a launchd bug where multi-part
options aren't properly split into separate arguments.