arc: z-order in the slice engine + gitops collapse tune (shard and cluster nests)

pilot/manifest-helm.json

@@ -6,6 +6,7 @@
    "name": "press",
    "title": "The chart",
    "blurb": "A function with holes - the template owns every structural decision, and renders whatever fills it.",
+   "z": 0,
    "points": [
     [
      28.09,
@@ -155,6 +156,7 @@
    "name": "contexts",
    "title": "Values contexts",
    "blurb": "One small file per cluster - names, addresses, sizes. The cluster's whole voice, values only.",
+   "z": 0,
    "points": [
     [
      24.11,
@@ -280,6 +282,7 @@
    "name": "renders",
    "title": "The renders",
    "blurb": "Same framework, different numbers - one function, many clusters. Review the render, not just the template.",
+   "z": 0,
    "points": [
     [
      54.4,
@@ -373,6 +376,7 @@
    "name": "gate",
    "title": "The schema gate",
    "blurb": "values.schema.json + required: a context missing a value fails at render time, in the pipeline.",
+   "z": 0,
    "points": [
     [
      52.58,