fix(rewrite): handle newline-separated commands

[jsiu93]

Closes #2191.

Summary

• Treat top-level newline and CRLF separators like other shell command separators during rtk rewrite.
• Rewrite every newline-delimited segment independently while preserving quoted newlines, heredoc passthrough, line-continuation collapse, and pipe group behavior.
• Cover hook permission checks so newline-separated commands are evaluated segment-by-segment before allow/deny/ask decisions.

Test plan

• cargo fmt --all -- --check
• cargo clippy --all-targets -- -D warnings
• cargo test --all --quiet
• Manual repro: target/debug/rtk rewrite "$(printf 'cd /tmp\ngrep -c x /tmp/f.txt\ngrep -c x /tmp/f.txt')"

[rtk-release-bot]

This pull request has been automatically marked as stale due to 90 days of inactivity. If this pull request is still relevant, please leave any comment (for example, "bump"), and we'll keep it open. Your contribution is very much appreciated — we're sorry we haven't been able to review it yet.

[jsiu93]

Closing this: the multiline rewrite landed upstream in #3319 (line-by-line rewrite via the quote-aware lexer, with &&/||/| continuation joining, CRLF preservation, and conservative passthrough for heredocs/control flow), and #2191 was closed after 952245d. That covers what this PR set out to do, and the branch has since drifted into conflicts with develop. Thanks for the review bandwidth.