feat: enhance superadmin dashboard overview

frontend/superadmin/src/service/ContentService.js

@@ -130,5 +130,21 @@ export const ContentService = {
                 reason
             }
         });
+    },
+    async getContentStatistics({ tenant_id, start_at, end_at, granularity } = {}) {
+        const iso = (d) => {
+            if (!d) return undefined;
+            const date = d instanceof Date ? d : new Date(d);
+            if (Number.isNaN(date.getTime())) return undefined;
+            return date.toISOString();
+        };
+
+        const query = {
+            tenant_id,
+            start_at: iso(start_at),
+            end_at: iso(end_at),
+            granularity
+        };
+        return requestJson('/super/v1/contents/statistics', { query });
     }
 };