Fix Oxygen Classic builder with custom fonts

[Jan-CoreBunch]

Summary

• HTML-escape the custom-font JSON injected into Oxygen Classic's ng-init attribute
• prevent font-family quotes from corrupting Angular initialization and stalling the builder
• add regression coverage for normal and special-character families, empty data, and disabled font integration

Validation

• PHPUnit: 32 tests, 61 assertions
• scoped PHPCS checks pass
• PHP syntax and diff checks pass
• manually verified Oxygen Classic loads and locally imported ABeeZee files return without console errors

Closes #19