fix(console): refine node health polling timeout and document CORS requirements

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Description

In web/app/node/page.tsx (lines 76-93), useNodeHealth polls node endpoints over plain HTTP with a rigid 8-second timeout:

const res = await fetch(`${NODE_BASE}/health`, {
  cache: "no-store",
  signal: AbortSignal.timeout(8000),
});

Root Cause

1. Aggressive Timeout: An 8-second network delay or temporary CPU load spike on the node instantly triggers an AbortSignal exception, flipping node health to DOWN and clearing UI state.
2. CORS Requirement: Browser fetch() calls to NODE_BASE fail with opaque network errors if remote witness nodes do not explicitly return Access-Control-Allow-Origin headers for the web app origin.

Expected Behavior

• Implement retry logic or exponential backoff before marking a node as DOWN.
• Add clear developer/operator documentation or warning banners regarding CORS configuration when connecting to non-local witness nodes.

Location

• web/app/node/page.tsx