[Bug] Add QueryError fallback when dashboard data fetches fail

[plind-junior]

Problem

When any dashboard API call fails, the affected panel stays stuck on its loading skeleton forever. useApiQuery has retry: false, so the first failure is terminal — users see a shimmer that never resolves and have no way to recover without a page reload.

Affected panels:

• StatsPanel
• MinerRatesTable
• OrderbookDepth
• EventFeed
• SwapTracker
• SwapDetailPage

Proposed change

Add a small QueryError component with a retry button, and show it in each consumer when the query has errored and has no data to fall back on.

// src/components/QueryError.tsx — icon + message + retry button, styled to match panels
<QueryError onRetry={() => refetch()} />

Each consumer gets one early return:

const { data, isLoading, isError, refetch } = useStats();
if (isError && !data) return <QueryError onRetry={() => refetch()} />;

Behavior

• First-load failure → QueryError replaces the skeleton. Retry re-runs the query.
• Refetch failure while data exists → silent; keep showing stale data (via keepPreviousData). Avoids flashing errors over working UI during transient blips.
• SwapDetailPage → QueryError rendered inline inside PageWrapper so header/layout stay.

Out of scope

• Global retry/backoff in useApiQuery (no change to retry: false).
• ErrorBoundary for render-time errors.
• Telemetry / error reporting hook.
• SSE reconnect timer fix.

Files touched

• src/components/QueryError.tsx (new)
• src/components/index.ts
• src/components/dashboard/StatsPanel.tsx
• src/components/dashboard/MinerRatesTable.tsx
• src/components/dashboard/OrderbookDepth.tsx
• src/components/dashboard/EventFeed.tsx
• src/components/dashboard/SwapTracker.tsx
• src/pages/SwapDetailPage.tsx