Clean up holes/gaps in sub-national regions (v0.15.0)

Part of #16

scripts/regions.test.ts

@@ -326,6 +326,48 @@ describe('regions.geo.json', () => {
     );
   });
 
+  it('has no small enclosed holes left (the v0.15 cleanup filled them); only real water bodies remain', () => {
+    // v0.15 cleanup (scripts/cleanup-regions.mjs): every enclosed hole (inner
+    // ring) smaller than the threshold was dropped so each region is solid;
+    // only genuine water bodies (holes >= the threshold) survive. The big real
+    // lakes (Great Lakes, Caspian, Aral, Lake Superior, …) were already
+    // dissolved by the v0.14 coarsening, so the surviving holes are few and
+    // large. This guards the fix: a re-introduction of the tiny artifacts
+    // (thousands of < threshold holes) fails here.
+    const HOLE_MIN_KM2 = 1000; // keep in sync with cleanup-regions.mjs HOLE_AREA_MAX_KM2
+    let holeCount = 0;
+    let smallHoles = 0;
+    let maxHole = 0;
+    for (const f of regions.features) {
+      const polys = f.geometry.type === 'Polygon' ? [f.geometry.coordinates] : f.geometry.coordinates;
+      for (const poly of polys) {
+        for (let i = 1; i < poly.length; i++) {
+          const hole = poly[i];
+          let lat = 0;
+          for (const [, la] of hole) lat += la;
+          const area = ringAreaKm2(hole, hole.length ? lat / hole.length : 0);
+          holeCount++;
+          if (area > maxHole) maxHole = area;
+          if (area < HOLE_MIN_KM2) {
+            smallHoles++;
+            if (smallHoles <= 10) console.log(`    small hole ${f.id} ≈ ${Math.round(area)} km2`);
+          }
+        }
+      }
+    }
+    expect(
+      smallHoles,
+      `${smallHoles} enclosed hole(s) below ${HOLE_MIN_KM2} km2 remain — the v0.15 cleanup should have filled them`,
+    ).toBe(0);
+    expect(
+      holeCount <= 20,
+      `${holeCount} holes remain — expected only a handful of real water bodies`,
+    ).toBe(true);
+    console.log(
+      `\n  enclosed holes: ${holeCount} remain (all >= ${HOLE_MIN_KM2} km2, largest ${Math.round(maxHole).toLocaleString('en-US')} km2) — small artifacts filled by the v0.15 cleanup`,
+    );
+  });
+
   it('sums to within [40%, 175%] of each country area (median in [70%, 130%])', () => {
     // The band is a planar-approximation sanity check. It is wider than a naive
     // [40%, 110%] because Natural Earth's admin-1 polygons are digitized