feat: add storage entry and attachment types

Introduces the Entry and Attachment types that the storage plugin will use as the source of truth for named storage volumes, replacing the colon-delimited mount strings stored under docker-options. Entries persist as JSON under config/storage/entries and validate against scheduler-specific rules; attachments persist via the property list and capture how an app uses an entry. The legacy migration name synthesizer is also added so existing colon-form mounts can converge on a deterministic legacy- entry name. Existing storage commands are unchanged in this commit.

plugins/storage/attachment_test.go

@@ -0,0 +1,33 @@
+package storage
+
+import (
+	"testing"
+
+	. "github.com/onsi/gomega"
+)
+
+func TestAttachmentValidate(t *testing.T) {
+	RegisterTestingT(t)
+
+	good := &Attachment{
+		EntryName:     "demo-data",
+		ContainerPath: "/data",
+		Phases:        []string{PhaseDeploy, PhaseRun},
+	}
+	Expect(good.Validate()).To(Succeed())
+
+	noEntry := &Attachment{ContainerPath: "/data", Phases: []string{PhaseDeploy}}
+	Expect(noEntry.Validate()).To(HaveOccurred())
+
+	noPath := &Attachment{EntryName: "demo-data", Phases: []string{PhaseDeploy}}
+	Expect(noPath.Validate()).To(HaveOccurred())
+
+	relative := &Attachment{EntryName: "demo-data", ContainerPath: "data", Phases: []string{PhaseDeploy}}
+	Expect(relative.Validate()).To(HaveOccurred())
+
+	noPhases := &Attachment{EntryName: "demo-data", ContainerPath: "/data"}
+	Expect(noPhases.Validate()).To(HaveOccurred())
+
+	badPhase := &Attachment{EntryName: "demo-data", ContainerPath: "/data", Phases: []string{"build"}}
+	Expect(badPhase.Validate()).To(HaveOccurred())
+}