fix: prevent setup-status hang with timeout/retry + retry UI

[0xNyk]

Summary

Fixes the setup page hang scenario where users can get stuck on "Checking Setup Status..." indefinitely.

What changed

• Added fetchSetupStatusWithRetry helper (src/lib/setup-status.ts) with:
  • bounded timeout per request
  • bounded retry attempts with small backoff
  • response shape validation
• Updated src/app/setup/page.tsx to use timeout+retry helper for initial setup check
• Replaced non-actionable fallback (return null) with a visible error state + Retry button
• Added unit tests for retry helper (src/lib/__tests__/setup-status.test.ts)

Why

Issue #456 reported setup flow hanging at "Checking Setup Status...". The prior code used a bare fetch('/api/setup') with no timeout/retry, and on failed check could also fall into a blank UI path.

Test plan

• pnpm exec tsc --noEmit
• pnpm exec vitest run src/lib/__tests__/setup-status.test.ts
• Manually reviewed setup error path now shows retry UI instead of empty screen

Fixes #456

[github-actions]

📸 Screenshot Drift Check

This PR modifies UI source files. Please verify whether the README screenshots need refreshing:

• docs/mission-control-overview.png — main dashboard
• docs/mission-control-agents.png — agents panel
• docs/mission-control-memory-graph.png — memory graph

Changed UI files

src/app/setup/page.tsx

See docs/SCREENSHOT-GUIDE.md for instructions on capturing and optimising screenshots.

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