Alert component for errors and notifications

There are places where the dashboard client uses alert() or console.error().

• console.error() messages obscure the error instead of alerting the user in a visble way in the UI.
• alert() is blocking and not stylistically consistent with other dashboard UI.
• Other scenario-specific notification mechanisms (like #8783) are are not suitable for general purpose use.

It would be better to show notifications and errors in a simple, consistent way that does not demand interaction, but nevertheless makes it visible in a clear but non-surprising way.

GitHub uses a banner at the top of the page for notifications and errors. The banner can be dismissed but also disappears automatically after navigating. See also Bootstrap examples here.

Requirements

• not modal - do not cover or block other interations
• dismissable
• allow multiple notifications (ok to overlay, and view one by one)
• works across admin dashboard, regular dashboard, and start-workspace UI
• loud (red?) notification for errors
• less-loud (orange?) notifications for non-error alerts
• visible on small screens (top of page, not bottom)

Typical use cases

• license errors in self-hosted deployments
  • #9971
  • #9972
• usage and billing notifications e.g. when approaching seat limit or free-usage limit
  • #9974
• websocket connection problems

Start by locating dashboard uses of alert() and console.error() across the admin dashboard, regular dashboard, and start-workspace UI. Review the listed requirements and related issues #8783, #9971, #9972, and #9974; done means a shared non-modal, dismissible notification experience that supports multiple error and non-error alerts across all three interfaces.