feat: sub-region-level territory — ownership, LLM and map at region granularity (v0.19.0)

Move territory from whole-country (ISO_A3) to individual sub-region id
granularity (PR 3 of #16):

- new server/regions.ts (turf-free): loadRegions (boot), expandTerritory
  (game creation), migrateTerritoryToRegions (legacy games on db.load),
  regionNamesFor / regionLabel (LLM prompt), graceful ISO_A3 fallback
- game creation expands each preset nation's ISO_A3 list to its sub-region
  ids; pre-v0.19 saved games migrate transparently on read (idempotent)
- LLM contract: territoryChanges gain/lose sub-region ids (one region at a
  time; gain moves out of the prior owner; lost-without-gainer = unowned);
  user prompt carries a top-level regions reference table
  ({id: 'name (parent)'} over the state's territory ids)
- WorldMap: choropleth fill per sub-region (countries can split between
  nations), ownership via properties.regionId through the shared
  mapFeatureOwner, flash lights exactly the changed features
  (featuresByRegionIds)
- deterministic stub: one region-level move per non-empty round (player
  annexes the lexicographically-first region of the first other nation)
- tests: new server/regions.test.ts (real geo + fallback + seams);
  map/engine tests re-pinned to region ids; scripts/regions.test.ts stays green

Measured full wwii-1939 user prompt (411 regions): ~24.7k chars / ~6.2k
tokens — far under the 80k frontier limit, so the full regions table is
always sent (no frontier-limited mode needed).

Part of #16

server/index.ts

@@ -19,6 +19,7 @@ import type { GameState } from '../shared/types';
 import { createLlmClient } from './llm';
 import { makeStubLlmClient } from './stub';
 import { askAdvisor, queueRoundItem, removeRoundItem, runTurn } from './engine';
+import { expandTerritory, loadRegions } from './regions';
 import { buildRegionMap } from './map';
 import { createPresetStore } from './presets';
 import { openDb, type Db } from './db';
@@ -41,6 +42,10 @@ function findRoot(): string {
 }
 
 const root = findRoot();
+// Load the sub-region geo once at boot (a graceful no-op, with a warning, when
+// the file is missing — the territory model then degrades to whole-country
+// ISO_A3 codes). Must run before the first game creation/load.
+loadRegions(root);
 const presetsDir = path.join(root, 'presets');
 const clientDir = process.env.CLIENT_DIST ?? path.join(root, 'dist');
 const dataDir = process.env.DATA_DIR ?? path.join(root, 'data');
@@ -116,7 +121,16 @@ app.post('/api/games', (req: Request, res) => {
     playerNationId: nation.id,
     turn: 1,
     date: preset.startDate,
-    nations: Object.fromEntries(preset.nations.map((n) => [n.id, deepClone(n)])),
+    // v0.19: territory is at sub-region granularity — expand each preset
+    // nation's ISO_A3 country codes into all their sub-region ids (a no-op that
+    // keeps the country codes when the region geo is not loaded).
+    nations: Object.fromEntries(
+      preset.nations.map((n) => {
+        const nation = deepClone(n);
+        nation.territory = expandTerritory(nation.territory);
+        return [n.id, nation];
+      }),
+    ),
     events: [],
     pending: [],
     version: 1, // the first saved revision; every later mutation bumps it