Shared LVGL UI building blocks that are reused by multiple screens and should remain portable across ESP Arduino, ESP-IDF, and future Linux LVGL targets.

Current contents

ui/app_screen.h
ui/app_runtime.h
ui/formatters.h
ui/components/two_pane_nav.h
ui/components/two_pane_layout.h
ui/components/two_pane_styles.h
ui/screens/* shared screen implementations
ui/assets/* shared icons/fonts/images

These files are the current shared UI contracts, reusable screens, and shared UI assets that no longer belong to a single legacy src/ui/* subtree.

Current boundary notes:

ui/app_screen.h defines the shared screen contract used by menu/runtime code
ui/app_runtime.h owns shared app-switching, menu-return, focus-group, and generic LVGL menu helpers
ui/formatters.h owns pure UI formatting helpers that do not depend on board state or persistence
battery, timezone, screenshot, display glue, map tiles, and other board/product-specific UI helpers now live under platform/esp/arduino_common