normalized PodView: shape-blind pod reads to match the shape-blind mutation api

[AviadHayumi]

follow-up to #341. the workload front door is shape-blind on the MUTATION and capability side , but Tree still returns ExtractedInstance with its mutually exclusive PodTemplateSpec / PodSpec / FragmentedPodSpec fields - so a consumer reading pod data still branches on which one is set ( the quickstart reads only PodTemplateSpec , which quietly skips fragmented-only workloads ).

the proposal : a normalized read view using the same vocabulary as PodPatch :

type PodView struct {
	SchedulerName     string
	PriorityClassName string
	Labels            map[string]string
	Annotations       map[string]string
	NodeAffinity      *corev1.NodeAffinity
	PodAffinity       *corev1.PodAffinity
	Containers        []corev1.Container
	// a field is zero when the definition cannot extract it
}

filled from whichever shape the definition has , exposed on the tree instance ( or via the workload ) , so read and write share one shape-blind vocabulary. ExtractedInstance stays in the power api.

out of scope for the first pr on #341 by agreement - tracked here.