feat: add settings management page

[baba-dev]

Summary

• extend the nav rail to surface a new Settings destination
• implement the Settings page with connectivity, appearance, maintenance, and backup controls backed by async updates
• hook the new page into the root view so it can be shown from the nav rail

Testing

• clang-format -style=file -i custom/ui/pages/ui_page_settings.c custom/ui/pages/ui_page_settings.h
• clang-format -style=file -lines=21:27 -i custom/ui/ui_nav_rail.c
• idf.py build (fails: command not found)

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https://chatgpt.com/codex/tasks/task_e_68cd142be2fc8324b2c0c62bd31a6b54