Address findings from the templates code review:
- Fix XSS in admin.html onclick handlers via data attributes
- Fix XSS in 5 edit page signal initializations via JSON serialization
- Fix register.html token exposure by moving to data attribute
- Add entity_icon, quick_notes_toggles, add_form_submit macros
- Replace hardcoded colors with design tokens (warning, error, success)
- Add warning design tokens to CSS theme
- Scope MutationObserver to main element
- Add defer to webauthn.js script tags
- Refactor login/register JS to arrow functions
- Guard lightbox script behind image_url check
- Fix else-if to elif in 5 templates
- Change btn-adjust to grey border with orange text and subtle hover
- Add font-family/font-size to .input-field for consistency
- Redesign desktop tabs: bordered, orange text, equal width, accent
border on active instead of filled background
- Redesign mobile tab selector: bordered dropdown with orange text,
rounded container, subtle active background
- Create shared tab_bar.html partial with desktop + mobile layouts
- Add CSS component classes (.tab, .tab-active, .tab-mobile variants)
- Replace divergent implementations in data.html and add.html
- Rename DataTab to Tab for shared use across templates
- Improve readability: darker inactive text, more spacing, hover states
