Add error handling for HTTP response writes

[alienx5499]

Problem

Multiple HTTP handlers call w.Write() without checking the returned error. Write failures are silently ignored, making it difficult to debug network issues or client disconnections.

Affected handlers:

• writeBeacon(), GetChains(), GetHealth(), GetBeaconIds(), GetInfoV1(), GetInfoV2() in routes_handler.go
• DisplayRoutes() in routes.go
• /chanz handler in metrics.go

Solution

Added error checking and logging for all w.Write() calls. Since HTTP headers may have already been sent when a write error occurs, we log the error but do not attempt to return an HTTP error status.

if _, err := w.Write(json); err != nil {
    slog.Error("failed to write response", "error", err)
}

Changes

• Added error handling for w.Write() in all HTTP handlers
• Error logs include context about which handler encountered the failure

Testing

• All existing tests pass
• Code compiles successfully