🧪 Add error handling test for YAML loading in validate_weapons.rb

[hahwul]

🎯 What: The testing gap addressed
The script scripts/validate_weapons.rb had a rescue => e block for catching YAML parsing errors when loading files from the weapons/ directory, but this behavior was untested.

📊 Coverage: What scenarios are now tested
A new test suite (test/test_validate_weapons.rb) using minitest/autorun has been added. It creates a temporary mock weapons/ directory, places a malformed YAML file inside, and executes the validation script as a subprocess. It then verifies that:

1. The script correctly catches the Psych::SyntaxError and prints the error message (e.g., matching "did not find expected key").
2. The script exits cleanly with a successful status code instead of crashing.

✨ Result: The improvement in test coverage
The error-handling path for reading weapon YAML files is now covered by automated tests, ensuring regressions (such as accidentally removing the rescue block) will be caught.

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PR created automatically by Jules for task 15305974614605038322 started by @hahwul

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