Prevent double-escaping of COMPOSER_AUTH and other JSON environment variables
by detecting valid JSON objects/arrays in realValue() and skipping quote
escaping entirely. This fixes broken JSON values passed to runtime services
while maintaining proper escaping for non-JSON values.
- Add JSON detection before escaping logic in EnvironmentVariable::realValue()
- JSON objects/arrays pass through unmodified, avoiding quote corruption
- Add comprehensive test coverage for JSON vs non-JSON escaping behavior
