Add 5 federation health checks: - CheckFederationRemotesAPI: verifies remotesapi port accessibility - CheckFederationPeerConnectivity: checks peer remote reachability - CheckFederationSyncStaleness: detects commits behind peers - CheckFederationConflicts: detects unresolved merge conflicts - CheckDoltServerModeMismatch: detects embedded vs server mode mismatch Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>