test(i18n): verify all locales have COMMITS_THIS_MONTH and VS_LAST_MONTH keys (JhaSourav07#2243)

## Description
Extends lib/i18n/badgeLabels.test.ts with a dynamic monthly view keys
describe block that asserts COMMITS_THIS_MONTH and VS_LAST_MONTH are
present and non-empty in every supported locale. Uses
it.each(Object.keys(labels)) so the tests automatically cover any locale
added in the future without needing to touch the test file.

Fixes JhaSourav07#1078

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- [ ] 📐 Pillar 2 — Geometric SVG Improvement
- [ ] 🕐 Pillar 3 — Timezone Logic Optimization
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Author: JhaSourav07

lib/i18n/badgeLabels.test.ts

@@ -70,4 +70,16 @@ describe('getLabels', () => {
       }
     });
   });
+
+  describe('monthly view keys', () => {
+    it.each(Object.keys(labels))('locale %s has a non-empty COMMITS_THIS_MONTH', (lang) => {
+      const locale = getLabels(lang);
+      expect(locale.COMMITS_THIS_MONTH).toEqual(expect.stringMatching(/\S/));
+    });
+
+    it.each(Object.keys(labels))('locale %s has a non-empty VS_LAST_MONTH', (lang) => {
+      const locale = getLabels(lang);
+      expect(locale.VS_LAST_MONTH).toEqual(expect.stringMatching(/\S/));
+    });
+  });
 });