Empty states, error states, and offline handling throughout the app

[Shieldxx]

What

Design and implement consistent empty states, error states, and offline/stale states for every major screen:

• Dashboard: no subscriptions yet, no providers configured, no Docker containers detected
• Spend tracking: provider stale (API failure), provider auth error, no key configured
• Docker: Docker not running, no containers, no AI containers detected
• Visual map: empty map with call-to-action

Offline handling: when a provider API is unreachable, show last-known data with a "last updated X ago" badge rather than clearing the screen.

Why

Empty states and error states are the difference between an app that feels broken and one that guides the user forward. They are also what new users see first.

Acceptance criteria

• Every screen has a designed empty state (not a blank white rectangle)
• Every network-dependent feature shows a stale indicator rather than hiding data
• Error messages are actionable ("Your Anthropic Admin key may have expired — check the Console") not generic ("Error")
• App launch succeeds with no network access and no Docker

References

MVP.md §5 Phase 7, §6 (Acceptance criteria #6)