Expand dead_code_handling to cover redundant conditions found by coverage tools

[hiroshinishio]

Summary

• Expanded the <dead_code_handling> section in coding_standards.xml to cover redundant conditions revealed by coverage tools (not just linters)
• Added a concrete before/after example: redundant truthiness checks inside an else block where the variable is guaranteed truthy
• This prevents GitAuto from trying to test unreachable V8 branches instead of refactoring the dead code

Context

foxden-admin-portal PR #483 failed because GitAuto tried to test unreachable branches caused by redundant conditions inside an else block. The existing dead_code_handling rule only covered linter-flagged dead code. Now it also covers coverage-reported unreachable branches.

Social Media Post (GitAuto)

Coverage flagged two uncovered branches. Our agent burned 50 iterations trying to test them, then OOM'd. They were unreachable - redundant null checks inside an else block where the variable was already guaranteed to exist. V8 counts those checks as branches even when they can never be false. New rule: fix the dead code, don't chase the test.

Social Media Post (Wes)

Agent burned 50 iterations trying to cover two lines, then OOM'd. Traced it - dead code. A redundant null check inside an else block where the variable is guaranteed truthy. V8 sees it as a branch that can never be false. Remove the check, 100% coverage. The answer was refactoring, not testing.