Read the zone tables from the asset pool, and name zones from their slugs

L62 moved zone-regions.json and groupings.json into data/tables/, so the tree
copies them into the asset pool and both plugins read one file. This fetches
them rather than importing: a relative import into another plugin's folder is
refused, and a per-plugin copy is the drift the single-source move exists to
prevent.

groupings.label is a definition, not a name, and using it as one would have made
the legend unreadable. Measured on the published file, the labels run from 7 to
206 characters and the long ones are the zone's member list — Tibet's names ten
provinces and three countries. Exactly one of the fourteen is a plain name. So
the tree names a zone from its slug, which is uniform by construction, and the
label is carried separately as the definition it actually is, for somewhere with
room to say what a zone contains.

The tree is built and counted; nothing filters on it yet. Mapping a group to a
zone still runs through the older partition, which places 69 groups in the wrong
printable zone, and that is the Driver's open question.

plugin-designs/gospel-internet/src/zoneData.js

@@ -0,0 +1,60 @@
+/**
+ * zoneData.js — fetch the published UPG-100 zone tables and build the legend's tree.
+ *
+ * The tables belong to upg100 and are now published: L62 moved them into data/tables/, so the
+ * tree copies them into the asset pool and both plugins read ONE file. That is why this fetches
+ * rather than imports — a relative import into another plugin's folder is refused by
+ * check:no-cross-plugin-imports, and a per-plugin copy is the drift the single-source move exists
+ * to prevent.
+ *
+ * FETCHED ONCE and shared, like the neighbour table beside it.
+ *
+ * ⚠ THE TREE IS READY; THE FILTER IS NOT. Mapping a GROUP to a zone still runs through
+ * admin-to-list.json, which exp measured as an older partition — 69 groups land in the wrong
+ * printable zone and 436 in Unassigned. That is the Driver's row 87. So this builds and counts
+ * the tree, and the caller must not filter rows on it until the fold lands.
+ */
+import { resolveAssetsBase } from '@map/utils/embedBase.js'
+import { buildZoneTree } from './zoneTree.js'
+
+let pending = null
+
+/** { nodes, allZoneIds, definitions } from the published tables. Rejects loudly. */
+export function loadZoneTree(cfg = {}, counts = {}) {
+  if (!pending) {
+    pending = (async () => {
+      const base = resolveAssetsBase(cfg)
+      const [zr, gr] = await Promise.all([
+        fetch(cfg.zoneRegionsUrl || `${base}/tables/zone-regions.json`).then(okJson),
+        fetch(cfg.groupingsUrl || `${base}/tables/groupings.json`).then(okJson),
+      ])
+      // ★ groupings.label IS A DEFINITION, NOT A NAME, and using it as one would make the
+      // legend unreadable. Measured on the published file: the labels run from 7 to 206
+      // characters, and the long ones are the zone's MEMBER LIST — Tibet's reads "Tibet
+      // Autonomous Region + Sichuan Province + Xinjiang Uyghur Autonomous Region + ... +
+      // North Korea". Only one of the fourteen is a plain name.
+      // So the tree's NAME comes from the slug, which is uniform by construction, and the
+      // label is carried separately as the zone's DEFINITION — which is what it actually is,
+      // and useful where there is room to say what a zone contains.
+      const definitions = {}
+      for (const [id, g] of Object.entries(gr || {})) if (g && g.label) definitions[id] = g.label
+      return { zoneRegions: zr || {}, definitions }
+    })()
+  }
+  return pending.then(({ zoneRegions, definitions }) => ({
+    zoneRegions,
+    definitions,
+    // No `labels` passed: buildZoneTree falls back to humanising the slug, which gives every
+    // zone a name of the same shape rather than one name and thirteen member lists.
+    nodes: buildZoneTree(zoneRegions, { counts }),
+    // EVERY zone the data can name, not just the ones filed under a region. The legend renders
+    // the difference as a named bucket; passing only the tree's ids would drop the unfiled ones
+    // with no error and no empty state — just a shorter list.
+    allZoneIds: Object.keys(zoneRegions),
+  }))
+}
+
+function okJson(res) {
+  if (!res.ok) throw new Error(`${res.status} ${res.url}`)
+  return res.json()
+}