fix(draw): show a 9,999.6 m² area as 1.0 ha, not 10000 m²

The draw hint picked m², ha or km² from the raw area and then rounded,
so 9,999.5 m² up to a hectare read "10000 m²" and about 999,500 m² up
to a square kilometre read "100.0 ha". It now rounds first, as the line
measure already does.

src/annotations/drawMode.js

@@ -215,9 +215,12 @@ export function formatMeasure(session) {
   }
   if (session.shape === 'area') {
     const m2 = ringAreaM2(session.vertices);
-    if (m2 >= 1e6) return `${(m2 / 1e6).toFixed(2)} km²`;
-    if (m2 >= 1e4) return `${(m2 / 1e4).toFixed(1)} ha`;
-    return `${Math.round(m2)} m²`;
+    // Round before each unit cut, as for a line. 9,999.6 m² was "10000 m²".
+    const whole = Math.round(m2);
+    const ha = (m2 / 1e4).toFixed(1);
+    if (whole < 1e4) return `${whole} m²`;
+    if (Number(ha) < 100) return `${ha} ha`;
+    return `${(m2 / 1e6).toFixed(2)} km²`;
   }
   return '';
 }