Race condition between polling (5s interval) and sign/reject operations
caused cards to flicker and reappear after being approved.
Fix:
- Pause polling during sign/reject API calls
- Resume polling after 1 second delay to allow backend state sync
- Apply same pattern to both signApproval and rejectApproval
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>