Add shared Icon primitive and controlled glyph vocabulary (Carbon, filled)

src/app/components/DatasetsModal.tsx

@@ -22,6 +22,7 @@ import { notify } from '../stores/NotificationStore';
 import { selectSelectedDataset, useDatasetStore, byModifiedDesc } from '../stores/DatasetStore';
 import { useSnippetStore } from '../stores/SnippetStore';
 import { SegmentedControl, type SegmentedOption } from './SegmentedControl';
+import { Icon } from './Icon';
 import styles from './DatasetsModal.module.css';
 
 /** Display label for a format (spec §05 → List item: JSON / CSV / TSV / TopoJSON). */
@@ -76,7 +77,7 @@ export function DatasetsModal() {
     <div className={styles.manager}>
       <div className={styles.listPane}>
         <button type="button" className={styles.newButton} onClick={handleNew}>
-          + New Dataset
+          <Icon name="add" /> New Dataset
         </button>
         <ul className={styles.list}>
           {ordered.length === 0 && (