Elect one fleet torrent seeder per AWS VPC via IMDS cloud_instance_meta.

Agents read vpc-id from EC2 IMDS on auth; the server scopes subnet_primary_seeder to vpc-id with /24 fallback, exposes VPC seeder badges, and documents cross-VPC gossip via peering/TGW.

server/internal/spreadrouter/router_test.go

@@ -123,25 +123,6 @@ func TestBuildSetsErasureLanesFlag(t *testing.T) {
 	}
 }
 
-func TestBuildSetsPreferFargateSeederWhenBurstActive(t *testing.T) {
-	in := Input{
-		TargetSubnets:      []string{"10.9.8"},
-		FargateBurstActive: true,
-		FleetAgents: []FleetAgentSnapshot{
-			{AgentID: "a1", Subnet: "10.9.8", Clearance: clearance.L2, Connected: true},
-		},
-	}
-	rt := Build(in)
-	rec, ok := rt.Recommend("10.9.8")
-	if !ok || !rec.PreferFargateSeeder {
-		t.Fatalf("route=%+v ok=%v", rec, ok)
-	}
-	hint := ToHint(rec)
-	if hint == nil || !hint.PreferFargateSeeder {
-		t.Fatalf("hint=%+v", hint)
-	}
-}
-
 func TestToHint(t *testing.T) {
 	hint := ToHint(RouteRecommendation{
 		TargetSubnet: "10.1.2", SeedAgentID: "a1", EgressAgentID: "a1", Score: 0.8,