feat(api): expose async backup/restore job status (fixes #7)

Backup and restore only enqueue a cluster Job; a later failure left its
only trace in that Job object, invisible without kubectl. Add
GET /api/v1/servers/{name}/jobs (owner-or-admin) projecting the newest
20 managed Jobs (felis-backup / felis-restore) as
running|succeeded|failed with message and timestamps. Nil reader -> 503
jobs_unavailable, mirroring the backup/restore feature gates. RBAC gains
jobs:list; OpenAPI parity updated.

cmd/felis/api.go

@@ -259,6 +259,7 @@ func cmdAPI(args []string, stdout, stderr io.Writer) int {
 		Builder:     builder,
 		Restorer:    restorer,
 		Backuper:    backuper,
+		JobStatus:   api.NewK8sJobStatus(cl, cfg.K8s.Namespace),
 		Files:       files,
 		Submissions: submissions,
 		Mailer:      mailer,