fix: check-issue delegates overhead comparison to check-rule-redundancy

[zazabap]

Summary

• The check-issue skill's Rule Check 1 (Usefulness) now invokes /check-rule-redundancy <source> <target> instead of manually parsing and comparing overhead tables
• Maps the redundancy verdict directly: Not Redundant → Pass, Redundant → Fail, Inconclusive → Warn

Test plan

• Run /check-issue on a [Rule] issue where a path already exists and verify it invokes /check-rule-redundancy
• Verify novel rules (no existing path) still pass without invoking the redundancy check

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.49%. Comparing base (0ac50ca) to head (78da5c9).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #593   +/-   ##
=======================================
  Coverage   96.49%   96.49%           
=======================================
  Files         204      204           
  Lines       28397    28397           
=======================================
  Hits        27401    27401           
  Misses        996      996           

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