feat(cli): add sort passthrough wrapper

[nightcityblade]

Summary

• Add a recognized rtk sort subcommand that delegates arguments and standard streams to native sort.
• Avoid the Clap parse failure and generic fallback round trip for rtk sort invocations.
• Fixes feat: add rtk sort wrapper (low priority) #3491.

Test plan

• cargo fmt --all --check && cargo clippy --all-targets && cargo test
• Manual testing: piped duplicate lines through target/debug/rtk sort -u and verified sorted, unique output; verified native invalid-option exit code propagation.

Important: All PRs must target the develop branch (not master).
See CONTRIBUTING.md for details.

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