[fix] return exit code 0 when settings check passes

[Fkuloff]

Previously CheckSettings always exited with code 1 and wrote JSON to stderr regardless of the validation outcome. Now it exits with 0 when the result is valid with no warnings and no message, and only writes the JSON structure to stderr on exit 1.

Before (always exit 1, always stderr):

replicas: 0 → exit: 1, stderr: {"valid":false,"message":"replicas cannot be 0","warnings":null}
replicas: 1 → exit: 1, stderr: {"valid":true,"message":"","warnings":null}
replicas: 2 → exit: 1, stderr: {"valid":true,"message":"","warnings":["replicas cannot be greater than 3"]}

After (exit 0 when fully valid, stderr only when needed):

replicas: 0 → exit: 1, stderr: {"valid":false,"message":"replicas cannot be 0","warnings":null}
replicas: 1 → exit: 0, stderr: empty
replicas: 2 → exit: 1, stderr: {"valid":true,"message":"","warnings":["replicas cannot be greater than 3"]}