test(cli): cover object remove purge help contract

[overtrue]

Summary

This change adds a focused help-contract test for the noun-first rc object remove command. The recent rm --purge work changed the shared remove argument surface, but the help-contract suite only covered the legacy rc rm entrypoint and did not verify that the noun-first alias exposed the same option set.

Problem

Users can reach object deletion through both rc rm and rc object remove. Because object remove reuses RmArgs, option changes such as --purge should remain discoverable through both entrypoints. Without a contract test on the noun-first command, a future clap wiring or command-group change could silently drop or alter that help surface while the existing rm help test still passed.

Fix

The test suite now asserts the rc object remove --help usage line, the inherited delete options, and a representative example. The new case includes --purge, which ties the test directly to the recent remove-command change while keeping the scope limited to help-contract coverage.

Validation

I could not run make pre-commit because this repository does not contain a Makefile or a pre-commit target. I ran the equivalent required checks from the repository instructions instead:

• cargo fmt --all --check
• cargo clippy --workspace -- -D warnings
• cargo test --workspace