- tile_button: large touch tile with accent bg + title + icon + value,
fires LV_EVENT_CLICKED (for home screen tiles)
- back_button: fixed bottom-left Zurueck button (LV_SYMBOL_LEFT),
large touch target, reused on all detail screens
- screen_base.h: Screen struct with create/show/hide/refresh/tick
lifecycle around an lv_obj_t root (replaces old ScreenId-only header)
- lv_conf.h: enable Montserrat 16/20/24 fonts used by the widgets