Fix test_preflight.sh (and thus the uat alias) to work in Basic/read-only mode: p4 push -n always fails with a permission error for the ftp user, which previously made test_preflight.sh (and uat, which chains test_preflight.sh && r) permanently unusable for Basic-mode clones.
Caught on the r9x86_64 canary during Task 1.3. Now skips the push check (with a clear message) when P4USER is ftp, since lacking push access is expected there, not a failure.
Agent: Claude Code, Model: Claude Sonnet 5 (claude-sonnet-5), operating as bot_Claude_Anthropic.