Bring in GenUI to build the settings page

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introduce Genui into Robrix

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Hello, @kevinaboos
In this PR, I've mimicked Element by using basic components from Genui to implement a settings page. This is just an initial version, so I haven't put much effort into beautifying the pages. The settings page currently supports only three screens: account_page, keyboard_page, and notification_page, with routing functionality between them.

In this PR, I modified the makepad-widget dependency from robrix since Genui needs to depend on the same makepad-widget library as robrix. I changed it to point to the corresponding repository to ensure Genui can be used correctly within robrix. In the future, if we introduce Genui into robrix, robrix will need to provide a stable makepad-widget dependency (ensuring Genui can depend on it reliably), making Genui easier to use for both us and other developers.