frontend: disable option to connect via tor proxy on ios

[thisconnect]

The Tor proxy can currently not be used on iOS. iOS restricts exposing local ports to other apps.

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• updating the Changelog
• writing unit tests
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• testing on multiple environments (Qt, Android, ...)
• having an AI review your changes

[benma]

We also need to disable it in the backend - users who already enabled it in the current iOS release would be stuck after this with no way of disabling it.

[benma]

Please re-target this pr to the release-v4.48.1 branch (which I just created) and put this changelog into v4.48.1, as it is fix to the v4.48.1 release.