feat(ui, alerts): add alerts from the UI

[flxwu]

What does this PR do?

Fixes # (issue)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• Chore (refactoring code, technical debt, workflow improvements)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (does not change functionality, e.g. code style improvements, linting)
• This change requires a documentation update

Mandatory Tasks

• Make sure you have self-reviewed the code. A decent size PR without self-review might be rejected.

Checklist

• I haven't read the contributing guide
• My code doesn't follow the style guidelines of this project (npm run prettier)
• I haven't commented my code, particularly in hard-to-understand areas
• I haven't checked if my PR needs changes to the documentation
• I haven't checked if my changes generate no new warnings (npm run lint)
• I haven't added tests that prove my fix is effective or that my feature works
• I haven't checked if new and existing unit tests pass locally with my changes

[flxwu]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
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Current dependencies on/for this PR:

• main
  • PR feat: add empty Alerts Page + mock API behind feature flag #2
    • PR feat(alerts): check user's total costs when ingesting generations #3
      • PR feat(alerts): db schema + alert when threshold is crossed #4
        • PR feat(ui, alerts): add alerts from the UI #5 👈

This stack of pull requests is managed by Graphite.