Handle empty validator set in monitoring

[giwaov]

Summary

• Preserve RPC error metadata in the wallet DS fetcher so callers can inspect server error codes.
• Treat validator-set error code 29 as an empty validator set in monitoring data loading.
• Keep other validator-set and monitoring fetch failures fatal.

Why

Fixes #431. A chain with no staked committee validators returns the canonical no-validators response, but the monitoring page treated it as a fatal RPC 400 and hid the other data that loaded successfully.

Testing

• npm run build
• git diff --check

[giwaov]

Hi maintainers, could you please take a look when you have a chance? This one addresses the reported monitoring-page failure for empty validator sets and keeps the rest of the monitoring data visible. I’m happy to adjust the scope if you’d prefer a different handling for code 29.