Introduces a custom Aura theme variant (amber daylight / aurora cyan
midnight, via -light/-dark token pairs) and a header toggle button to
switch between them at runtime, using the Vaadin 25 ColorScheme API
(Page#setColorScheme, @ColorScheme) rather than the older Lumo-only
theme-attribute pattern. The choice is persisted in a cookie so it
survives reloads and future sessions without any client-side script,
and is restored flash-free on the next visit via an
IndexHtmlRequestListener.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BNL5syWGwM7KnFcuZeEKQ1
pitfriedrich