* feat: add macOS setup script for Jamf deployment
Adds scripts/pmg_setup_install.sh that installs/updates pmg (via
Homebrew or GitHub releases), runs pmg setup install, and optionally
enables cloud sync with credentials stored in macOS Keychain.
* feat: add --from-env flag to pmg cloud login
Allows non-interactive credential import from SAFEDEP_API_KEY and
SAFEDEP_TENANT_ID environment variables. Fails explicitly if either
is missing. Used by the setup script for Jamf deployments.
* refactor: use cloud.NewEnvCredentialResolver for --from-env
Use the dry library's env credential resolver instead of reading
env vars directly, keeping env var ownership in the shared library.
* update DRY
* update go to 1.25 back
