fix: redact finding evidence in outputs

[CoderDeltaLAN]

Summary

• Redact finding evidence in JSON and Markdown payload construction.
• Add regression coverage for secret-like values appearing in finding evidence.
• Preserve the existing structured finding model and governance rule behavior.

Scope

• CLI payload redaction only.
• Test coverage only.
• No release, README, CHANGELOG, CI, dependency, packaging, or branch protection changes.

Local verification

• 93 tests passed.
• Real JSON output redacts secret-like evidence.
• Diff is limited to src/agent_rules_kit/cli.py and tests/test_cli.py.
• v0.1.0 tag/release verified intact before push.