FAB login. Fix asset URLs and missing alert

[vincbeck]

Resolves #47565

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[vincbeck]

This resolves all front-end errors on the login page except one:

Uncaught TypeError: moment(...).tz(...).format is not a function
    at r (main.ec1d38d994d72bb083cd.js:2:826)
    at u (main.ec1d38d994d72bb083cd.js:2:2623)
    at HTMLDocument.<anonymous> (main.ec1d38d994d72bb083cd.js:2:4808)
    at e (jquery-latest.js:2:30038)
    at jquery-latest.js:2:30340

Looking into it but that can fixed in a separate PR