Flip the client to region-key resolution + region names in the dossier (v0.19 P1 of #16)

- src/lib/regions.ts (new): cached, turf-free same-origin fetches of
  /region-keys.json (feature id -> key) and /regions.geo.json (id -> name) so
  WorldMap and NationPanel share one fetch each.
- WorldMap.tsx: stamps each feature's properties.regionKey (from the manifest,
  by its stable id) and resolves owner / flash / hover / click from that key via
  the shared mapFeatureOwner; the per-region flash lights the exact sub-region
  whose owner changed; click carries only the sub-region name.
- NationPanel.tsx: territory chips show the region's human name (falling back
  to the raw key) with the key in the title / data-attr.
- App.tsx: the selected-region dossier label drops the now-unused parent code.

src/App.tsx

@@ -591,12 +591,11 @@ function GameScreen({
   const [viewingId, setViewingId] = useState(game.playerNationId);
   // When the dossier target was set by a map click, remember which sub-region
   // was clicked, for a small label in the dossier. The label shows only the
-  // region's name — the static parent-country code (which never updates on a
-  // transfer) is no longer displayed, though the info object still carries it.
-  // Cleared when the user picks a nation via the manual Inspect select.
-  const [selectedRegion, setSelectedRegion] = useState<{ parent?: string; name?: string } | null>(null);
+  // region's name. Cleared when the user picks a nation via the manual Inspect
+  // select.
+  const [selectedRegion, setSelectedRegion] = useState<{ name?: string } | null>(null);
   const focusNation = useCallback(
-    (id: string, info?: { parent?: string; name?: string }) => {
+    (id: string, info?: { name?: string }) => {
       setViewingId(id);
       setSelectedRegion(info ?? null);
     },