[codex] Surface dashboard fetch source health

[Dreamstore2046]

Summary

Closes #213.

Surfaces per-source dashboard fetch health instead of silently hiding failed data:

• adds a generic useFetch<T> hook that tracks data, error, lastSuccessAt, and loading state for each source
• wraps the agent info, spending, and transactions fetch paths with per-source health tracking
• adds a header health chip that turns red when any source is failing
• exposes a tooltip/title listing the failed source and error message
• adds a component test that simulates a failed spending source and asserts the chip turns red with the right tooltip copy

Validation

• npm test -- dashboard/src/__tests__/dashboard-header-health.test.tsx
• npm test -- dashboard/src/__tests__/dashboard-header-health.test.tsx dashboard/src/__tests__/settings-tab.test.tsx
• npx tsc --noEmit --target ES2022 --module ESNext --moduleResolution bundler --allowImportingTsExtensions --esModuleInterop --allowSyntheticDefaultImports --strict --skipLibCheck --types node,vitest dashboard/src/hooks/fetch-health.ts
• git diff --check

Notes:

• A TSX-focused tsc command for the header/hook files is blocked in this checkout because React type declarations are not installed/resolvable (react/jsx-runtime / @types/react), matching the existing dashboard dependency-resolution limitation.

[vercel]

@Dreamstore2046 is attempting to deploy a commit to the Harrison Eze's projects Team on Vercel.

A member of the Team first needs to authorize it.