Migrate to checker-sdk-go v1.3.0 with standalone build tag

The SDK split the HTTP server scaffolding into the new
checker-sdk-go/checker/server subpackage and CheckRule.Evaluate now
returns []CheckState. Update main.go to import server and call
server.New, switch the rule and the package-level Evaluate helper to
the new slice return type, and isolate the interactive form code
behind the standalone build tag so plugin/builtin builds skip
net/http and html/template entirely.

checker/evaluate.go

@@ -9,7 +9,7 @@ import (
 // Evaluate folds findings into a single CheckState. The status is the
 // highest severity observed: any Crit makes the whole result Crit, any Warn
 // makes it Warn, otherwise OK.
-func Evaluate(data *DelegationData) sdk.CheckState {
+func Evaluate(data *DelegationData) []sdk.CheckState {
 	status := sdk.StatusOK
 	var crit, warn, info int
 	for _, f := range data.Findings {
@@ -37,7 +37,7 @@ func Evaluate(data *DelegationData) sdk.CheckState {
 		msg = fmt.Sprintf("Delegation of %s: %d critical, %d warning, %d info", data.DelegatedFQDN, crit, warn, info)
 	}
 
-	return sdk.CheckState{
+	return []sdk.CheckState{{
 		Status:  status,
 		Message: msg,
 		Code:    "delegation_result",
@@ -49,5 +49,5 @@ func Evaluate(data *DelegationData) sdk.CheckState {
 			"parent_ds":      data.ParentDS,
 			"child_serials":  data.ChildSerials,
 		},
-	}
+	}}
 }