refactor: migrate dashboard pages to useApi

[xx7412421-cloud]

Closes #9

Summary

• migrate pairs and events dashboard pages from bespoke useEffect/apiGet state to the shared useApi hook
• map loading, error, and ok states to Spinner, role="alert", empty states, and list rendering
• add useApi coverage for success, error, null path, and unmount-during-fetch cancellation
• add page tests for loading, success, empty, and error states on both migrated pages
• document the shared read-only data fetching pattern in the README

Validation

• npm ci
• npm test -- src/lib/tests/useApi.test.tsx src/app/pairs/page.test.tsx src/app/events/page.test.tsx --runInBand
• npm test -- --runInBand
• npm run build
• npm run lint

[mikewheeleer]

hey @xx7412421-cloud, thanks for the effort here 🙏 issue #9 isn't assigned to you though — to keep the campaign fair and avoid duplicate work, please claim/get assigned to it first, then open your PR. closing for now; would love to see it back once it's assigned to you 🙌