feat: sign in to connectors from their switches and close OAuth popups reliably

[themaherkhalil]

• Sign-in popups close as soon as the login is done, wherever the popup lands: the SDK's oauth() and connectLogin share one wait that reads the login while the popup is open, and oauth() fails instead of hanging when the popup is closed or blocked
• Both popups start with ?disableRedirect=true, so the backend ends the sign-in on a page that closes itself instead of loading an app inside the popup
• The client signs in through the SDK's oauth() instead of its own copy
• Connectors settings: switching on an app whose account is not connected signs in and then turns on that app; each account asks to "Sign In with Microsoft" or "Sign In with Google"
• Add Connectors to the composer's plus menu, opening the Connectors settings page
• Show the instance's version and build time in a footer on the General settings page

[snyk-io]

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