fix: guard object preview fullscreen on webkit

[cxymds]

Pull Request

Description

Fix the object preview modal fullscreen controls for iOS Safari/WebKit by guarding fullscreen entry/exit behind compatible helpers instead of assuming the standard Fullscreen API is always available.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Code refactoring
• Performance improvement
• Test improvements
• Security fix

Testing

• Unit tests added/updated
• Manual testing completed

node --test tests/lib/object-preview-source.test.js
./node_modules/.bin/eslint components/object/preview-modal.tsx tests/lib/object-preview-source.test.js
./node_modules/.bin/prettier --check components/object/preview-modal.tsx tests/lib/object-preview-source.test.js

Checklist

• Code follows the project's style guidelines
• Self-review completed
• TypeScript types are properly defined
• All commit messages are in English (Conventional Commits)
• All existing tests pass
• No new dependencies added, or they are justified

Related Issues

Closes #129

Screenshots (if applicable)

Additional Notes

This PR intentionally only includes the preview modal fullscreen compatibility fix so the WebKit crash can be reviewed independently from broader browser-page hardening changes.