fix: dnf support in setup-node + setup-aws, node label t3.medium

- setup-node: detect dnf (Amazon Linux) alongside apk/apt-get
- setup-aws: detect dnf for official installer
- node Spot bumped to t3.medium (4GB) — Docusaurus OOM'd on t3.small

orchestrator/dispatch/main.go

@@ -101,7 +101,7 @@ type spotConfig struct {
 
 var labelToSpot = map[string]spotConfig{
 	"go":     {InstanceType: "t3.small", MaxPrice: "0.02"},
-	"node":   {InstanceType: "t3.small", MaxPrice: "0.02"},
+	"node":   {InstanceType: "t3.medium", MaxPrice: "0.04"},
 	"docker": {InstanceType: "t3.medium", MaxPrice: "0.04"},
 	"deploy": {InstanceType: "t3.micro", MaxPrice: "0.01"},
 	"godot":  {InstanceType: "t3.medium", MaxPrice: "0.04"},