Fleet UI: Calendar settings design updates

[RachelElysia]

Issue

Updates to #17444
Part of #17230

Screenshot

Checklist for submitter

If some of the following don't apply, delete the relevant line.

• Manual QA for all new/changed functionality

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 65.33%. Comparing base (9861f6e) to head (07ef1a7).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #17869   +/-   ##
=======================================
  Coverage   65.33%   65.33%           
=======================================
  Files        1204     1204           
  Lines      110022   110022           
  Branches     2585     2585           
=======================================
  Hits        71880    71880           
  Misses      32640    32640           
  Partials     5502     5502           

Flag	Coverage Δ
frontend	51.46% <ø> (ø)

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[jacobshandling]

👀

[jacobshandling]

Also, let's please:

• Success/error flash messages should have "."s at the end, unless that decision was changed recently in which case we should replace all of them.
• Update API Key JSON and Primary domain validation error messages to use "completed" instead of "present"

[jacobshandling]

Approving so we can merge before freeze, please address those comments as unreleased bugs, which they are!