Complete Greatest covers and use Japanese navigation label

test/greatest.test.js

@@ -7,6 +7,7 @@ test('curated manga catalog has unique identities and ordered five-year periods'
   const catalog = loadCatalog();
   assert.equal(catalog.periods.length, 13);
   assert.equal(catalog.entries.length, 106);
+  assert.ok(catalog.entries.every(entry => /^https:\/\//.test(entry.cover)), 'Every catalog title has cover artwork');
   for (const [index, period] of catalog.periods.entries()) {
     const entries = catalog.entries.filter(entry => entry.period === period);
     assert.ok(entries.length >= 5 && entries.length <= 10);