Replace archived YAML dependency

Switch direct YAML usage from gopkg.in/yaml.v3 to go.yaml.in/yaml/v4, the maintained YAML org fork of the archived go-yaml repository.

Update README dependency and mirroring links so the documented source repository matches the module used by the application.

src/core/store.go

@@ -7,7 +7,7 @@ import (
 	"runtime"
 	"strings"
 
-	"gopkg.in/yaml.v3"
+	"go.yaml.in/yaml/v4"
 )
 
 type Store struct {

src/core/store_test.go

@@ -4,7 +4,7 @@ import (
 	"strings"
 	"testing"
 
-	"gopkg.in/yaml.v3"
+	"go.yaml.in/yaml/v4"
 )
 
 func TestJobsYAMLDoesNotPersistRuntimeNoise(t *testing.T) {