v0.27.0 (#44): LLM-placed named map point markers

- shared: 8 MarkerTypes + MARKER_TYPE_INFO (label/color/glyph); MapMarker;
  GameState.markers (required, [] at init); TurnResult.markers {add,remove};
  MarkerSpec/MarkerInfo; FNV-1a 4-char markerId; MAX_MARKERS=400.
- data: new public/region-centroids.json (1,800 anchors = largest-part centroid
  + spread ~0.1x min-bbox) built by new idempotent scripts/build-region-centroids.mjs.
- server: regions.ts centroid loader (public/ then dist/); engine applyTurnResult
  marker ops (remove -> owner-recompute -> add, jitter, cap, never throws);
  prompt documents the contract; buildUserPrompt carries markers; stub marker-free.
- client: WorldMap symbol layer rendered as canvas per-type icons (glyph CDN dead);
  hover tooltip shows name; click focuses owning nation.
- tests: 168 -> 189 (centroids script, regions centroids, db legacy, engine markers).

server/db.test.ts

@@ -25,6 +25,7 @@ function makeState(id: string): GameState {
     version: 1,
     unowned: [],
     pendingNationOps: [],
+    markers: [],
   };
 }
 
@@ -97,6 +98,17 @@ describe('openDb', () => {
     db.close();
   });
 
+  it('(v0.27 #44) a legacy row saved before the markers field existed loads with it defaulted to []', () => {
+    const db = openDb(':memory:');
+    const legacy = makeState('legacy');
+    delete (legacy as { markers?: unknown[] }).markers; // a pre-v0.27 save (field absent)
+    db.save(legacy);
+    const loaded = db.load('legacy');
+    expect(loaded).not.toBeNull();
+    expect(loaded!.markers).toEqual([]);
+    db.close();
+  });
+
   it('delete removes a game by id and reports absence otherwise', () => {
     const db = openDb(':memory:');
     db.save(makeState('a'));