fix: clarify RC005 axis-count help

[Akimbo92i]

Summary

• Clarifies RC005 launch-contract mismatch help so axis counts are spelled once.
• Avoids recommending a nonexistent three-axis index formula for domain-3 contracts.

Changes

• Adjusted RC005 help construction for domain-2 and domain-3 launch contracts.
• Added a domain-3 lint sample fixture.
• Extended CLI assertions for strict text, findings JSON help, and SARIF output.
• Added an Unreleased changelog entry for the diagnostic wording fix.

Testing

• cargo fmt --all --check passed during implementation.
• cargo test -p cargo-reconverge --test check_cli lint_samples_report_all_codes_and_gate_the_exit passed during implementation.
• cargo clippy --workspace --all-targets -- -D warnings passed during implementation.
• cargo test --workspace passed during implementation.
• git diff --check passed during implementation and PR preparation.

Related Issue
Fixes #100