feat(export): compute sns rankings from full contact timeline

src/pages/ExportPage.scss

@@ -2370,6 +2370,18 @@
     padding: 6px 0;
   }
 
+  .sns-dialog-rank-loading {
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    gap: 6px;
+    min-height: 28px;
+    padding: 4px 0 8px;
+    font-size: 12px;
+    color: var(--text-secondary);
+    line-height: 1.5;
+  }
+
   .sns-dialog-rank-row {
     display: grid;
     grid-template-columns: 20px minmax(0, 1fr) auto;