Resolve all security vulnerabilities, bug fixes, and print watermarking configurations based on product review

refactor: safe editor folding, centralize api client headers, sync cloud preferences, and add tests

fix: resolve overflowing header controls and layout responsiveness in editor & main toolbar

refactor: Modularize frontend App.tsx into custom hooks and components and resolve Vite import.meta types

feat(editor): implement advanced print settings and spellcheck

feat: add syntax highlighting and preference sync