fix: handle closed stdout while listing snapshots

[magrathean-uk]

Summary

• use fallible stdout writes for snapshot output
• treat an expected BrokenPipe as clean early termination
• cover the shared rewrite dry-run output path and JSON writer path

Fixes #1878

Validation

• cargo fmt --check
• cargo clippy --locked --all-targets --features release -- -D warnings
• cargo test --locked --lib