Integrate First-Party Mode Toggle into Ads Settings Form

[hussain-t]

Feature Description

Add the <FirstPartyModeToggle /> component to the Ads settings forms, enabling existing users to opt into First-party mode. The toggle will default to "off" and can be enabled if desired.

If either the FPFE health check or script access check fails, the toggle will be disabled and grayed out, displaying an error message instructing users that additional server configuration is needed to enable First-Party Mode.

For details, refer to the Design Doc.

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Implementation Brief

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