### Summary
Add dark mode support to the BootstrapAdminUi bundle using Bootstrap 5.3
color modes.
### Features
- Theme toggle button (sun/moon) in the navbar
- Persistent preference via localStorage with prefers-color-scheme
fallback
- Anti-flash inline script applied before page paint
- Login page logo adapts to active theme
- SCSS refactored to use CSS custom properties (--tblr-*) throughout
- ApexCharts re-renders on theme change via MutationObserver
### Changes
- Add theme-switcher.js script
- Add theme.html.twig anti-flash hookable in #stylesheets (priority 200)
- Add theme_switcher.html.twig navbar button hookable
- Refactor _body.scss, _sidebar.scss, _tom-select.scss with include
color-mode() mixin
- Replace hardcoded colors in _accordion.scss, _filters.scss,
_form.scss, _loader.scss, _navbar.scss
- Update statistics_chart.js to use CSS vars and re-render on theme
change
- Update login logo template to support both light/dark variants
