install.ps1 now delegates every destination to Sync-ManagedDestination
instead of a blind copy-and-backup loop, so repeated installs are cheap
and safe by default.
Adds -Client and -Platform parameters so CI or scripts can run fully
non-interactively (install.ps1 -Client Both -Platform Windows); both fall
back to the existing interactive prompts when omitted. Plugin updates now
require an explicit -UpdatePlugins switch instead of always updating
already-installed plugins, so a configuration update never silently
changes third-party plugin code.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>