Add UART and Modbus configuration options to settings menu

[zkoalexey]

• Updated README.md to include UART and Modbus settings details.
• Added UART and Modbus menu items in jxd-r6-e1eth-lcd-eth.yaml and jxd-r6-e1eth-lcd-wifi.yaml.
• Created new files for UART and Modbus settings menu items.
• Implemented persistent storage for UART baudrate and Modbus address settings, with immediate effect on changes.
• Updated jxd-r6-e1eth-base.yaml to include new settings files.

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Note

Adds display-menu options to configure UART baud rates and Modbus server address with immediate, persisted changes, and integrates them into R6 configs and docs.

• UI/Menu:
  • Add UART and Modbus settings to display menu via include/jxd-r6-uart-menu-items.yaml and include/jxd-r6-modbus-menu-items.yaml.
• Config/Settings:
  • New include/uart-settings.yaml: runtime-selectable baud rates for jxm_uart1/jxm_uart2 (persisted, immediate effect).
  • New include/modbus-settings.yaml: configurable Modbus server address (persisted, immediate effect) applied to id(jxd_modbus_server).
  • Update include/jxd-jxm-uarts.yaml: document runtime baud configuration.
  • Update include/jxd-jxm-modbus-auto.yaml: clarify default address is configurable.
• Device Config Integration:
  • Include new menus in JXD/jxd-r6-e1eth-lcd-eth.yaml and JXD/jxd-r6-e1eth-lcd-wifi.yaml.
  • Wire settings into base via include/jxd-r6-e1eth-base.yaml (uart_settings, modbus_settings, reorder packages).
• Docs:
  • README.md: document UART baudrate and Modbus address configuration, ranges/options, and immediate effect.

^{Written by Cursor Bugbot for commit d099ca9. This will update automatically on new commits. Configure here.}