[WIP] Fix JavaScript tests for better accuracy

[Copilot]

Fix JavaScript Tests

• Identify failing tests in add_labels.test.cjs
• Update test expectations to match new error message format
  • Fix test: "should fail when target is '*' but no item_number in labels item"
  • Fix test: "should fail when target is '*' and issue_number in item is invalid"
• Run tests to verify fixes - All 1694 tests passing
• Run full validation with make agent-finish

Original prompt

Fix javascript tests

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