Add --rules-dir option to load rules from custom directory

[Aswinr24]

Issue

Right now the CLI auto detects the rules directory via a few fixed locations (bundle, package path, current working directory). This makes it hard to:

• run syshardn against a custom ruleset without forking the repo,
• keep multiple rulesets and switching between them,
• run CI/tests against a temporary rules directory in a clean way.

Proposed feature

Add a --rules-dir PATH option that overrides rules auto-detection.

• When provided, the CLI should use only that directory (no fallback to auto-detected locations).
• If the directory is missing/invalid or contains no rules, return a clear error and a non-zero exit code.